Sentence Correction

Proponents of artificial intelligence say they will be able to make computers that can understand English and other human languages, recognize objects, and reason as an expert does-computers that will be used to diagnose equipment breakdowns, deciding whether to authorize a loan, or other purposes such as these.


(A) as an expert does-computers that will be used to diagnose equipment breakdowns, deciding whether to authorize a loan, or other purposes such as these

(B) as an expert does, which may be used for purposes such as diagnosing equipment breakdowns or deciding whether to authorize a loan

(C) like an expert-computers that will be used for such purposes as diagnosing equipment breakdowns or deciding whether to authorize a loan

(D) like an expert, the use of which would be for purposes like the diagnosis of equipment breakdowns or the decision whether or not a loan should be authorized

(E) like an expert, to be used to diagnose equipment breakdowns, deciding whether to authorize a loan or not, or the like

OA: C

can someone explain why D is wrong? thank u so much!
and I would also like to ask the use of " ---- "