Problem:

Question: Why does the nuclear import receptor only release its cargo protein in the nucleus, and not in the cytosol?

A) Because Ran-GDP binds the receptor in the nucleus
B) Because Ran-GTP is more abundant in the nucleus due to the localization of Ran-GEF in the nucleus
C) Because the receptor hydrolyzes GTP in the nucleus, changing to a lower energy conformation with less affinity for the cargo
D) Because the nuclear localization signal is removed from the cargo protien in the nucleus
E) Because the receptor has less affinity for the cargo in the nucleus due to the lower pH there.

Please select correct answer and also provide explaination.