why choose d but not e?

yanda

Byron possessed powers of observation that would have made him a great anthropologist and that (makes his letters as a group the rival of)  the best novels of the time.
d, makes his letters as a group the rival of
e, makes his letters a group which is the rival of

shellyaaa

make sth sth 这里是make his letters / the rival of the best novels of the time.
as a group 是修饰 his letters，表示作为一个整体。