The free$-$rider problem in international defense means that the world has too $q,$ defense against aggression.

Nations try to overcome the free$-$rider problem in international defense by $q,$

A$.$ much; having U$.$S$.$ military bases in foreign countries

B$.$ much; having private firms provide defense

C$.$ little; signing treaty agreements to reduce weapons or to develop new weapon systems

D$.$ little; raising taxes