The boy was last seen being playing by the riverside with other boys 改错

the boy------(can ,could,was could)not swim last year The missing boy was last seen ___ near the river.A.playing　 B.to be playing　　C.play　　D.to play为什么选A?see的被动语态不用还原to吗?为什么不用B, The boy was last seen being playing by the riverside with other boys 改错 when the boy was Can you see the boy? the boy was seen to come in the room.see 只有see sb.doing/ see sb.do 此句能用了see to do 改错：Although the boy spent much time playing,but he was successful at last The winner of photo competition last time was an 18-year-old boy改错 Was the boy heard ____with others from 8 to 9 last night(argue) 什么时候用see sb.done?顺便问一下He was last seen swum in the river. the last time to see 改为同义句：I was afraid to see the snake in the fores改为同义句：I was afraid to see the snake in the forest last summer.I was afraid _____ _____ _____ the snake last summer. The ____ (miss)boy was last seen ____ (play)near the river .missing ; playing不是see sb do sth看见某人过去或经常做某事,而see sb doing sth是看见某人正在做某事吗?这里也没有正在的含义啊,请详解这两个空为什么 The boy was monster The boy was a monster The little boy was last seen______football by the river.A.to play B.play C.played D.playing Last week the missing boy was seen_____by the lake填什么?A walk B walking C walked D have walked the missing boy was last seen ___near the housea playingb to play为什么不能选B而选A I joined in a race .I overtook the second boy at last.I was the champion.翻译成中文