The correct answer is: [E]: "will have graduated" .
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This tense, which is the "future perfect" tense, is formed by using "will have" and followed directly with the past participle of the verb.
Note that the "future perfect tense" is used to describe an "action" that
"will occur" [sometime in the future] before some other action [takes place].
By the time the troops arrive, the co11mbat group will have spent several weeks waiting.