An insulator can do which of the following? conduct charge through it. become positively or negatively charged. transfer protons. transfer charge only to other insulators.

The correct answer is:
Become positively or negatively charged

In fact, an insulator is a material where charges cannot move freely. Therefore, it can be positively or negatively charge (for example, if it is rubbed against another object, the insulator can remain with an excess of charge), but it cannot transfer charge to other objects.