This is from GMATTER

A patient accusing a doctor of malpractice will find it difficult to prove damage if there is a lack of some other doctor to testify about proper medical procedures.

A. if there is a lack of some other doctor to testify

B. unless there will be another doctor to testify

C. without another doctors testimony

D. should there be no testimony from some other doctor

E. lacking another doctor to testify

The OA is C, my answer was D.
Can anyone explain why D is wrong?