Large corporations are often more successful than small companies at

You are right. Fixed. Thank you.

Thanks.

A. Large corporations are often more successful than small companies at retaining employees....................looks fine


B. Larger corporations are often more successful at retaining employees than smaller companies..................'with high potential' in non-underlined part should modify employees instead of smaller companies


C. Large corporations, often more successful than small companies at retaining employees.................Fragment. Not a complete sentence.


D. A large corporation often more successfully retains employees than does a small company....................Same as B


E. Large corporations are often more successful as small companies at retaining employees.........................Wrong comparison.

IMO OA should be A

IMO A
Large corporations are often more successful than small companies at retaining employees with high potential and at providing opportunities for professional development.

A. Large corporations are often more successful than small companies at retaining employees
B. Larger corporations are often more successful at retaining employees than smaller companies
C. Large corporations, often more successful than small companies at retaining employees
D. A large corporation often more successfully retains employees than does a small company
E. Large corporations are often more successful as small companies at retaining employees

Placement is the key here.
after the underline part we have -->with high potential and it is modifying employees so in no case we can have smaller companies with high potential. For that reason lets eliminate B and D
Let tackle C now, I am looking at it and I don't see any verb here -->C is gone . It is a fragment

Coming to E don't we need a than after more for the comparison. -- > E is gone too.