Urban officials want the census to be as accurate and complete as poss

Use of 'for the reason' is unidiomatic. A ,B out.
Between D and E ,the answer is D,the number is not changed by the amount of fund but the opposite so affect is correct use.
also it is 'the number' so it will be affectS.

should be D. didnt find any error in it

Official Explanation:

The best answer will start with because. The initial phrase of A is wordy, that of B is unidiomatic, and that of C does not precisely establish causal relationship. Also, amount is incorrect; number refers to a group of countable members, whereas amount is for undifferentiated masses such as sand or water. There is no subject-verb agreement in A (amount . . . affect), C (amount . . . effect), or E (numbers . . . effects); moreover, the proper verb here is affects, not effects. In E, numbers and areas should be singular, not only to agree with the verb but also to refer precisely to the sum total of low-income people in each region where the census is conducted. Choice D is the best answer.

A - amount of people - incorrect

B - same error as in A

C - same error as in A

D - the number is singular and is used correctly- correct

E- the numbers is plural and hence incorrect usage.

(A) for the reason that the amount of low-income people in a given area affect - Wrong: 1) Should use "number" instead of "amount" to refer to countable noun "people". 2) SV mismatch: "amount" should be used with "affects" and not "affect"

(B) for the reason because the amount of low-income people in a given area effects - Wrong: 1) Should use "number" instead of "amount" to refer to countable noun "people". 2) These words "reason because" together are redundant.

(C) in that the amount of low-income people in given areas effect - Wrong: 1) Should use "number" instead of "amount" to refer to countable noun "people". 2) SV mismatch: "amount" should be used with "affects" and not "affect"

(D) because the number of low-income people in a given area affects - Correct

(E) because the numbers of low-income people in given areas effects - Wrong: 1) Idiom: Should be "the number of" instead of "the numbers of".

Just two basic points:
1. We don't describe people as the amount of people. It has to be only ' the number" A, B and C are out.
2. The subordinate clause requires a verb. 'Effects' in E is not a verb. It is a plural noun. Therefore only D.

Subtle one.
First split: Subject verb agreement: amount of / number of --> singular.
Second split: Affect vs effect. Affect is impact and usually a verb, effect is result of a change and usually a noun.

There are plenty of other faults with A, B, and E as well. But the above will quickly and convincingly give you correct D

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