joealam1 wrote:One study found that although government policy and the industrial sector in which a company operates can influence its productivity and financial strength, management decisions have at least as great an impact on a company's performance.

A) Management decisions have at least as great an impact
B) Decisions by management have a great impact
C) Manager decisions impact greatly
D) Decisions by a company's management impact greatly
E) What a company's management decides has a greater impact

Is the answer D

parallelism
government policy , industrial sector and management decisions

it should be A

It is not a question of parallelism but rather of meaning.

Note that - 'although government policy and the industrial sector in which a company operates can influence its productivity and financial strength' is a subordinate clause.

You need a main clause to go along with it.

Look at this example from GMATPrep-
Although energy prices have tripled in the United States over the last two years, research indicates that few people have significantly reduced the amount of driving they do or made fuel efficiency a priority when shopping for cars.

This does not mean that 'energy prices' and 'research' are parallel. All it means is that the clause following 'although' is subordinate to the main clause. Also note that although indicates contrast.

A means that either management decisions have the same impact on company's performance as government policy and industrial sector have
or they have a greater impact than government policy and industrial sector have.

We do not know whether this impact is great or not (all we know is that it is greater than or equal to impact from government policy and industry sector).

B, C and D change the meaning of original sentence by suggesting that management decisions have a great impact.

E changes the meaning by suggesting that management decisions have a greater impact (the original sentence says greater than or equal to).
Also, note that A is more parallel than E.