Which of the Situations Below Will Enhance Microtubule Shrinkage

Which of the situations below will enhance microtubule shrinkage?

A) addition of a drug that inhibits GTP exchange on free tubulin dimers
B) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers
C) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules
D) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin