Which is a common tactic used in proxy wars?

a. encouraging opposing powers’ citizens to emigrate
b. sponsoring wars of liberation and revolutions
c. controlling another country secretly
d. buying weapons in preparation for domestic warfare

The correct answer should be b.sponsoring wars of liberation and revolutions

This is a common tactic. One country sponsors rebels in another country which destabilizes it and therefore destabilizes its relationship with the country with which the sponsoring country originally wanted to go to war with.