i don't think that the use of except is that big of a deal here, i think its just a particle used to stress exclusion. C is incorrect because it uses 'students' which is plural and then uses a singular verb - 'has'. if it was ''student's '' it would have been correct. answer D is correct because it uses correct tense and 'all of' instead of 'al'

thanks for editing the post. C sounds pretty good to me after you clarified that there student is singular. i am really perplexed as to what might be wrong with it.

This is from Kaplan 800. There was something to do with the meaning of the sentence, but I don't understand the explaination from the book. There is no typo at this time.

I picked C.
I don't anything wrong with it on the other hand I find "Requirements for Graduation" much better than "Graduation Requirements"

Isn't there a modifer problem with D?

Except for one history class and one biology class, the student has fulfilled all of his graduation requirements.

'Except for one history class and one biology class' is modifying 'student', which I think is wrong

comments?

The perfect sentence could have read The student has fulfilled all of his graduation requirements except for one history class and one biology class.

But this is not so.

I always try to rearrange the question stem in order to try out different options. OK, since it is not given as above, and following same thoughts i share with patrickpui, the closest, for me is D, though it seems a silly construct. Surely, these folks can do better!

I just checked Kaplan800 and indeed don't find the explanation very convincing. I think each of C and D could be "improved".

D clearly has a modifier problem. Here, the history and biology classes are incorrectly modifying "the student". IMO, D would be better re-written as follows:

Except for one history class and one biology class, the graduation requirements were fulfilled by the student.

See the difference? The prepositional phrase before the comma now clearly modifiies the "graduation requirements"

As for C, the problem does not lie in "all of the requirements" vs "all the requirements". As a matter of fact, both can be used and through a google search, I found many universities (ie Darden) who used "fulfilled all the requirements" without the "of"; for GMAT purposes, the omission of "of" seems even more concise. C actually seems to be best although it could be less good for 2 minor reasons:
1- For aesthetic reasons and sentence flow, it seems better to start off an "except" sentence with the exception first. I'll give you two examples and you'll perhaps see after a quick glance.
ie Except for Richard, nobody understood
ie Nobody understood except for Richard
Usually, after "understood", we would except a complement to follow, not an "except" phrase.
2- Another minor reason could lie in the wordiness of saying "one class in history" which could be shortened to "one history class". We eliminated the preposition "in" to make it more concise.
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Best Regards,

Paul