请选择CBA8{'Z(j-U:?'V)h-]/N:l2jListen!The boys _______ singing.2{,d1Z9|*o7N.x7A,y8}
A. is2{,d1Z9|*o7N.x7A,y8}
B. am2{,d1Z9|*o7N.x7A,y8}
C. are2{,d1Z9|*o7N.x7A,y8}