Using a computer model to estimate future productivity, the accuracy of such an estimate is higher than that achieved using more subjective methods.

A) Using a computer model to estimate future productivity

B) By the use of a computer model to estimate future productivity

C) If a computer model is used to estimate future productivity

D) With a computer model for estimating future productivity

E) Estimating future productivity with a computer model

There are a couple problems with choice A.
1) What follows the modifying phrase "Using a computer model to estimate future productivity" should be the thing that use the computer model.
2) "such an estimate" does not refer to anything.

b) "the accuracy of such an estimate" cannot use a computer

d) "with a computer model" this nonsensically implies that the accuracy along with a computer model. Additionally, the progressive tense (-ing) is only appropriate for two things that happen simultaneously or continue to happen. This is not one of those cases.

e) "Estimating" implies that the accuracy was estimating the future productivity.

c) The right choice.
"Such an estimate" refers to the previous "to estimate".
Uses the if . . . than structure and is parallel.

Thanks gmatutor for the lucid explanation