At the last charity drive only 68 percent of the pledges

As the two part around ";" should be part of the same logical construct, C by use of "had" connects to the previous part.

C also reflects the correct tense for the sentences (paid/had ..)

C. more than one hundred others had not made any

Answer: C

D is the most concise. C uses past perfect, without any real need for it.

Can we use a past tense and a past perfect tense each in two different sentences separated by a semi-colon.
I hope my question is clear. Right now i just can't think of a pertinent example.

As a rule, on the GMAT, it is recommended that past perfect tense be avoided unless one needs to show a chronological sequence between events.

For example:

He ate ham and sausages for breakfast yesterday
NOT
He had eaten ham and sausages for breakfast yesterday.

(NOTE: both are grammatically correct, but the GMAT believes that the second sentence does not need the past perfect tense).

Another example:
He had eaten ham and sausages when sat down for breakfast yesterday.

The above sentence justifies the use of 'had', since it tells us he ate the ham and sausages before he sat down for breakfast.

There is no rule involving the semi-colon in this case, to the best of my knowledge.

Will go with D.

I think "Had" is not required here. We are already talking about past hence no need for "had" here

Separate the two phrases into sentences to test if the past perfect can be used here... NOPE.

(D) survives