Answer: I would contend that the right answer is the E) "... since they provide fascinating evidence about the creative processes in which this great Modernist engaged."
Explanation: Just to elaborate a little bit on the answer, it can be added that the other options feature sentences that end with a preposition ("engaged in"), and although this is permissible in the English language, it is not the most formal option. In the example, a good way to correct it is to replace it by "in which." I would suggest changing the sentence so it reads "Although the author himself declared them unpublishable, the first appearance in print of 40 poems by T.S. Eliot is a significant event, since they provide fascinating evidence about the creative processes in which this great Modernist engaged."
D. both Mowgli and Shere Khan have vowed to hunt the other down
Because he is not having the best birthday he is also probably sad because Having the blues means your sad.
