A compound known as X-Gal is widely used in molecular genetic research. When wild-type (normal) E. ...

A compound known as X-Gal is widely used in molecular genetic research. When wild-type (normal) E. coli is grown on medium containing X-Gal, the bacterial colonies turn blue. In contrast, when lacZ mutants are grown on medium containing X-Gal, the bacterial colonies remain their normal white color. What is X-Gal likely to be?
A) a compound chemically similar to glucose
B) a compound chemically similar to galactose
C) a compound chemically similar to lactose
D) a compound that cannot be transported into lacZ mutants
E) a compound that can only be transported into lacA mutants