okay here is my understand:
galileo must be used in the first part as a subject because "he" needs an antecedent; therefore, d and e are out.
next phase is to choose the best verb tense.
X didnt make Y, but on hearing that Y had been made, X built his/her own Y.
the first part says that X didnt make Y, but he made it after hearing that Y had been made. Had been is used to emphasize that Y was made sometimes in the past before X make it and still in progress, later he made his own. A is right. B is wrong and will catch most of he students attention as a right option. C is wrong, did must be used.
I am sorry i worst in explaining things..

hope this helps..Cheers
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