A new law proposed by privacy advocates would increase the amount of

Official Explanation

Creating a filter: in the original sentence, the conditional tense in "would increase" is appropriate; the law isn't in effect yet, so the effect is expressed in the conditional tense. However, the verb tense in the phrase "have been allowed to build" isn't correct; it indicates, contrary to the intended meaning, that the law is changing what carmakers were allowed to do in the recent past.

Applying the filter: choice (B) has the same problem. Choices (C) and (E) fail to use "would." Could such the indicative (normal) verb tense be correct here? It could be a reasonable intended meaning of a sentence similar to this one that the bill will pass with certainty and the effect will take place. However, we can infer that the intended meaning of the sentence in this question is different, because it refers to a "proposed" law. The law, evidently, will not necessarily pass, so the intended meaning is conveyed by the conditional tense, not by the indicative tense. Furthermore, (C) uses the unidiomatic "tint amount," while (E) uses the unidiomatic "allowed for windows by carmakers."

The correct answer is (D).

A new law proposed by privacy advocates would increase the amount of tint that carmakers have been allowed to build into the windows of their vehicles

A)would increase the amount of tint that carmakers have been allowed to build -" Till now they have been allowed to build and not still what they are building "
B)would increase the tint amount that carmakers have been building - Tint amount is unidiomatic as amount of tint
C)will increase the tint amount carmakers are allowed to build - will makes the certainty that law will pass and Same as B
D)would increase the amount of tint that carmakers are allowed to build - Correct
E)will increase the amount of tint allowed for windows by carmakers - by carmakers - wrong meaning

A - 'have been allowed to build' indicates that amount of tint already built in the windows (in the past) would be increased - OUT
B - 'increase the tint amount' does not seem logical, 'have been building' indicates that amount of tint already built in the windows (in the past) would be increased - OUT
C - 'increase the tint amount' does not seem logical, 'that' is missing, 'will' indicates certainty - OUT
E - 'tint allowed by carmakers' - changes the meaning - OUT

D does not include any of these errors - CORRECT