there is a boy singing in the park 为什么sing要ing

there is a boy singing in the park 为什么sing要ing singing in the rain sing为什么要加ing? There is a boy in the room.He is singing合并为一句 单项选择.Listen!The boy is ____ .A、sings B、sing C、singing listen!she（）in the classroom.A.is singing B.sing C.to sing D Is there a forest in the park? there is a nature park in the Is there a forest in the park There is a slide in the park. is there a river in the park? Does your father singing?sing为什么要加ing? we sat around singing songs.为什么sing要加ing?