(a) and (e) are both grammatically ok, but (e) is ambiguous. therefore, if this problem were official - which it's most certainly not (it's a terrible question) - the correct answer would be (a).

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the story:

(e) is ambiguous.

it has 2 possible meanings:

(1) small investors have the same info about the companies' health as the larger investors have (this is clearly the intended meaning)

(2) small investors have the same info about the companies' health as they have about the larger investors.

the second is a bit strange, but you can't use "common sense" to get rid of ambiguity. if a sentence is ambiguous, it's ambiguous; tough luck.

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(a) is not ambiguous, because of the extra "do" (which is totally well placed; see next post)

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to whoever said this:

as do the isn't correct

whoa, no. totally wrong.

it is completely ok to have helping verbs before the noun in the 2nd half of a parallel construction such as this one.
in fact, it's not only ok, it's often REQUIRED.

example:

i know more about shakespeare than my brother
--> incorrect. ambiguous. we can't tell whether this means "i know more about shakespeare than my brother knows about shakespeare" (the presumably intended meaning) or "i know more about shakespeare than i know about my brother".

i know more about shakespeare than my brother does
i know more about shakespeare than does my brother
--> both correct.

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i know more about shakespeare than my brother, who has never taken a course in british literature
--> incorrect. ambiguous.
for the same reason as above.

i know more about shakespeare than my brother, who has never taken a course in british literature, does
--> incorrect. can't separate "my brother" from the HELPING VERB "does" with a modifier this long.

i know more about shakespeare than my brother does, who has never taken a course in british literature
--> incorrect. you can NEVER separate a noun from a "comma + who/which" modifier.

i know more about shakespeare than does my brother, who has never taken a course in british literature
--> correct.
this is the ONLY place where it's acceptable to put this "does".

for the same reason, "as do the..." is the best way to write (a), since it resolves the ambiguity and is properly placed.