A) is not right because "engaged in" is as if the author engaged in battle with the processes
B) 'it' is wrong because it should refer to the 'poems' and not the appearance. It is the 'poems' which are providing evidence. The 'appearance' cannot
C and D are not right. I cannot tell the exact english rule for the improper use of 'because' here but I know that a sentence starting with 'although' cannot be completed by 'because'.
Only E survives. Good subject agreement and concise in the usage of 'engage'