Desertification, the situation when desert conditions spread into prev

Official Explanation:

According to the sentence, desertification is the spread of desert conditions into previously arable land and is a global ecological problem. The given sentence is flawed in at least two ways. First, the word situation is an unsuitable choice since it refers to something static rather than a process, which desertification is. A second flaw concerns the way in which when is used. Here, the clause seems meant to modify situation, seeming to function as an adjectival modifier, whereas clauses introduced by when are normally adverbial modifiers, and adverbial clauses are not appropriate modifiers of nouns. A clause introduced by when may modify a noun referring to a period of time, but situation is not such a noun.

A As explained above, this answer choice is incorrect.
B The word condition is unsuitable because of its static connotation, given that desertification is a process. The clause introduced by where seems meant as an adjectival (relative) clause modifying condition but fits awkwardly in that role; although where can be taken as a rough equivalent to in which in casual speech, a condition is not a place, so a where-clause cannot appropriately modify the noun condition in formal writing.
C This version is unnecessarily awkward. The word condition is unsuitable because of its static connotation, given that desertification and spreading are processes. It is unclear whether the adjectival modifier spreading … lands modifies desert or condition.
D One flaw here is the redundancy of previously with the past tense was. Overall, because of the vagueness of where, this answer choice does not make clear that desertification involves the replacement of previously arable land with desert. The expression where land was previously arable is an unnecessarily wordy substitute for into previously arable land.
E Correct. This answer choice provides the clearest and most economical version of the sentence. The locution spread … into accurately and concisely characterizes the process of desertification.

The best answer is E.

Desertification, the situation when desert conditions spread into previously arable lands, is a global ecological problem threatening the life-support-systems of the planet.

[a]situation when desert conditions spread into previously arable lands -- "when" is not the correct relative pronoun here as exact time of happening is not indicated or important
condition where the desert spreads into previously arable lands -- "where" is wrong too since this is not a physical location
[c]condition of the desert spreading into previously arable lands -- very wordy
[d]spread of desert conditions where land was previously arable -- same error as B
[e]spread of desert conditions into previously arable land -- CORRECT, short appositive describing Desertification process

So, Answer is [b]E

Desertification, the situation when desert conditions spread into previously arable lands, is a global ecological problem threatening the life-support-systems of the planet.

We know that we have to use the modifier so stick to absolute modifier form or any better grammatically correct modifier .

A. situation when desert conditions spread into previously arable lands -(Desertification could be a process but never a situation . using time stamp here makes no sense when we talk about facts ) Reject
B. condition where the desert spreads into previously arable lands - (here again we are talking about location = where. a condition is not a place .Don't use such words to explain a process /facts )reject
C. condition of the desert spreading into previously arable lands - Reject (here spreading ....lands is an ing modifier which can refer to condition or the desert .Why? because this modifier makes sense in meaning with both the nouns hence its ambiguous )
D. spread of desert conditions where land was previously arable - USING WAS makes this no longer a modifier .reject
E. spread of desert conditions into previously arable land - simple and unambiguous absolute modifier CORRECT ans is E .

A. situation when desert conditions spread into previously arable lands - 'when' should refer to time frame.

B. condition where the desert spreads into previously arable lands - where should refer to location, and not a condition.

C. condition of the desert spreading into previously arable lands - continuous tense - spreading- incorrect

D. spread of desert conditions where land was previously arable - same as B

E. spread of desert conditions into previously arable land - correct

If you like explanation, do like.

A. situation when desert conditions spread into previously arable lands: Firstly, it is not a situation. Desertification is more of a process. Also, 'when' is not used correctly, 'in which' probably would have been better
B. condition where the desert spreads into previously arable lands: 'where' is generally used for location
C. condition of the desert spreading into previously arable lands: same error as in option A, it is not a condition but a process. Also, 'condition of desert spreading' has made the sentence awkward
D. spread of desert conditions where land was previously arable: same error as in option B
E. spread of desert conditions into previously arable land: Bingo!!

Please give kudos if the explanation helps!!

Sentence Meaning:
Desertification
- is the spread of desert conditions into previously arable land
and
- is a global ecological problem.

A. situation when desert conditions spread into previously arable lands
Wrong:
1. the word situation is an unsuitable choice since it refers to something static rather than a process
2. flaw concerns the way in which when is used, it refer to time

B. condition where the desert spreads into previously arable lands
Wrong:
1. The word condition is unsuitable because of its static connotation, given that desertification is a process.
2. a condition is not a place, so a where-clause cannot appropriately modify the noun condition in formal writing.

C. condition of the desert spreading into previously arable lands
Wrong:
1. The word condition is unsuitable because of its static connotation
2. Desert spreading - Tense error

D. spread of desert conditions where land was previously arable
Wrong:
1. Redundancy of previously with the past tense was. Overall, because of the vagueness of
2. Usage of word "where" describing location than process

E. spread of desert conditions into previously arable land
Correct - Intended meaning " process explained spread of desert conditions into previously arable land"

The best answer is E.

Where in GMAT is for actual places, so we can eliminate B and D
Desertification is not a condition or situation.. its a more eventual thing. So A and C are out.
Leaving us with E