Below is the full text of the question, but the question whose answer I crave for learning is the 24th question.

Bill Clinton’s main legacy for race relations in the United States is that he helped to sustain and accelerate the desegregation of the higher circles of American life. On the psychological plane, he gently pushed the white American public to accept something that (21) ---- many whites today is (22) --- more in question than one would like to believe: that blacks really can be equal or (23) ---- superior to whites in performing the most crucial and difficult tasks demanded by our society. George W. Bush contributed to this process when he (24) ---- Colin Powell as Secretary of State. Through his appointment of blacks and genuine friendships with them, Clinton has deepened this (25) ---- in American life.


A) appoints

B) had appointed

C) has appointed

D) appointed

E) would appoint

The official answer is D, but I wonder whether B is possible or not. I think B may be the answer as well.

Thanks in advance

Emotion: smile
By the way, how can I stop "Normal 0 21 false false false TR X-NONE X-NONE" from appearing in my posts?
It happened only once and Powell is no longer S of S so, simple past tense.
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When shows simultaneity, both should be simple past, that's the first reaction you should have
As Marius says, the contribution of Bush is the appointment of Powell. The two are merely different descriptions of the same fact, so there cannot be any question that the same tense is needed in both descriptions. ... contributed ... when ... appointed ...

Thank you all for the clarification

Emotion: smile
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The official answer is D. I agree with them depending on collocation between contributed and appointed [past simple and past simple] in one sentense.

But if we talk about what had happened first and what followed, we can use past perfect tense.
In the case above, if we want to mention about the time that when George W. Bush 'had appointed' Colin Powell as Secretary of State, he contributed to this process. I think it's possible to answer.