Why Does the Isoleucyl-TRNA Synthetase Use Two Types of Proofreading

Multiple Choice

Why does the isoleucyl-tRNA synthetase use two types of proofreading mechanisms to ensure its accurate aminoacylation?

A) It is not a very precise enzyme.
B) It is a very big enzyme.
C) Isoleucine is very hard to distinguish from valine,since they differ only by a single methylene group.
D) Isoleucine is very difficult to distinguish from glycine.
E) Isoleucine can spontaneously turn into phenylalanine.