Am I right

The answer for this question is "e". In this sentence, I understand "making his travels difficult" modifies the Andes Mountains. I would like to know whether there is a possibility for this type of clause to modify a subject. In this sentence, the subject is Hiram Bingham.

Hiram Bingham, explorer and professor of South American history, first crossed the Andes Mountains in February 1909, the wettest month of the year, which makes his travels difficult.

a) which makes his travels difficult
b) that had made his travels difficult
c) which should have made his travels difficult
d) because it made his travels difficult
e) making his travels difficult