we can use both structures:
S + V + multiple number (twice, three times, four times, etc) + as + adj/adv + as + noun/pronounor
S + V + multiple number + more + adj/adv + than + Noun/pronounboth of them are correct
So, it's based on the context and other factors of a sentence when it comes to choose a correct answer
In your example:
(A) minority graduates are nearly four times more likely than
are other graduates
in planning to practice -->
are is ungrammatically used here. Besides, in planning to practice seems wordy and illogical because of the continuous tense of verb plan here is not suitable(B) minority graduates are nearly four times more likely than other graduates
who plan on practicing -->
this choice adds a sub clause "who plan on ... areas" into the sentence, unnecessarily modifying for a sub Noun as other graduates, while the main Noun minority graduates is not strongly and clearly modified: what is minority graduates 4 times more likely than other graduates for ?
(C) minority graduates are nearly four times as likely as other graduates to plan on practicing -->
the best: correct structure ... four times as likely as ... , to plan on practicing is idiomatic, clear and a clear modification for the main noun minority grads than in (B)(D) it is nearly four times more likely that minority graduates are rather than other graduates will plan to practice -->
many errors !!!
(E) it is nearly four times as likely for minority graduates ... -->
also many errors