2道单选题The missing boy was last seen ___ near the river.A.play
2道单选题 The missing boy was last seen ___ near the river.A.playing B.to be playing C.play D.to play 为什么不选B? He was often heard___ the International.A.sing B.to sing C.sang D.to be singing 为什么?能不能添singsing? 这两道题感觉差不多啊.