The moving charge in the wire causes the compass to deflect; this is because

a. the moving charge induces a magnet field
b. the energy of the charge pushes on the compass
c. the electrons heat up the wire, causing the compass to deflect

The answer is A. the moving charge induces a magnet field .

The moving charge induces a magnetic field

Explanation:

According to Faraday's Law, the moving charges in a closed circuit (conductor) induces a magnetic field.

There is a potencial difference called electromotive force, wich is proportional to the magnetic flux through a surface. Matematically this coud be written as

where is the EMF, and is the magnetic flux (the derivative on t means that the magnetic flux is changing in time).

This means that the moving charges, generates an EMF that is proportional to the magnetic flux change.

Therefore, A is the correct answer.