At the turn of the twenties century, forest covering as much

main verb is required hence C,D,E remain
Elephants are countable hence as many as is required only D

At the turn of the twenties century, forest covering as much as 90 percent of Thailand and accomodating as many as 300,000 elephants, a third of them domesticated and performing various essential tasks.

A) covering as much as 90 percent of Thailand and accomodating as many as 300,000 elephants, a third of them

B) covering as much as 90 percent of Thailand accomodated as much as 300,000 elephants, a third of them

C) covered as much as 90 percent of Thailand and accomodated as much as 300,000 elephants, a third

D) covered as much as 90 percent of Thailand and accomodated as many as 300,000 elephants, a third of them

E) covered as much as 90 percent of Thailand and accomodating as many as 300,000 elephants, with a third of them

"as many as " is correct here because "as many as" is modifying elephants which are countable.
Option A , D , E are left.

Option A is incorrect because "accommodating as many as 300,000 elephants" is a verb-ing modifier and it has no logical entity ( some noun etc ) to modify here.

Option E is also incorrect due to the same reason mentioned above.

Option D uses "covered " and "accommodated " and both have been used as verbs. So parallel and correct.

Is my explanation correct ? VeritasKarishma

look at choice e.
even if " accomodating" is changed into " "accomodated", choice e is still wrong because " with a third of them..." grammatically work as an adverb. this means "with a third..." must modifies the preceding clause. but there can not be any logic meaning relation between the preceding clause and "with a third...". so, no logic meaning relation means an error.

I did a search on this question and I believe it is from GWD, who is a Chinese guy with, supposedly, something like photographic memory. So, supposedly, this is a real GMAT question

In my GMAT Prep 4, I got this somewhat modified version of above question - for example, check option B

At the turn of the twentieth century, forest covering as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, a third of them domesticated and performing various essential tasks.

A) covering as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, a third of them

B) covering as much as 90 percent of Thailand accommodated as much as 300,000 elephants, and a third of them were

C) covered as much as 90 percent of Thailand and accommodated as much as 300,000 elephants, with a third

D) covered as much as 90 percent of Thailand and accommodated as many as 300,000 elephants, a third of them

E) covered as much as 90 percent of Thailand and accommodating as many as 300,000 elephants, with a third of them

OA is D

I wrongly marked option B. For the benefit of everyone I thought to add why I was wrong. It is very interesting to check last underlined part of the sentence.
1. covering is correctly modifying 'forest' 2. accommodated correctly modifies 'forest covering 90% of Thailand' 3. after comma we have and --> means we need independent clause 4. a third of them were --> looks correct to me (a third of them belongs to 300,000 elephants) except that the verb 'were' followed by 'domesticated and performing' brings trouble

I think domesticated and performing should be logically used as modifiers and not as verbs. The verb 'were' and 'and' requires parallelism that is not present between 'were domesticated' and 'were performing'.

Option D correctly uses domesticated and performing as modifiers. Hence, Option D is better than Option B.
Takeaway for me --> non-underline part is important.

Could you please explain the approach?