First grammar. This is question of idiom and modification
Idiom: ‘Attribute to’ is the right idiom, ‘attribute as’ is wrong. So choices C and E are gone.
Modification; The underlined part ‘but in attributing smoking to tobacco companies’ is supposed to be done by the attorneys who are suing the tobacco companies. But instead of attorneys, you find only ‘smokers’ which turns the clause into one of misplaced modification. So choices A and B that have ‘but in arrtibuting to’ are worng This leaves us with choice D only, which uses a passive voice to match the passve voice in the latter part to render the clause without modificiation error and make it more //.
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The smokers are not attributing the smoking to tobacco companies - the lawyers are. Therefore A, B, and C are out.

Between D and E, D wins on account of being clear and direct as compared to E.

D it is.
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ABC lose becos of mis-modification; E loses because of using wrong idiom, ‘attributed as’ rather than ‘attributed to’.
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The tricky part of this question is to notice that (A) - (C), all mistakenly modify 'the smokers.' In this case, 'the smokers' are not doing any of the attributing. The 'told that they' shows that some other agent is responsible for the attributing.

By using the conditional 'if' we fix the problem of modification.

Finally, to choose between (D) and (E), we rely on the proper idiom: attribute to.

Therefore (D) wins out.

Hope that helps .
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The sentence as written contains a modification error. The modifying phrase "in attributing smoking to tobacco companies" is intended to modify "attorneys." It is the attorneys who are attributing smoking to tobacco companies. But the placement of the phrase makes it modify what comes after it—"the smokers." Eliminate (A).

A quick scan of the choices reveals a 3-2 split, with (A), (B), and (C) using the same "in attributing ...," which incorrectly modifies "the smokers," while (D) and (E) change the phrase to "if ... attributed."

(A), (B), and (C) can be eliminated right away, since they contain the modification error noted above. Compare (D) and (E).

Between (D) and (E), (D) is more concise and direct. If X is attributed to Y is sufficient, there is no need to use the wordier and more roundabout Y is attributed as the cause of X. Therefore, (D) is correct.

TAKEAWAY: A modifying phrase at the beginning of a sentence or independent clause modifies the noun that comes right after the comma. Make sure that this noun is really what the sentence intends to modify.
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