Listen,the bird is singing in the tree.listen 为什么不用加ing?

Listen,the bird is singing in the tree.listen 为什么不用加ing? Listen,the bird_____(singing,is singing)in the tree. listen to the bird in the tree. listen,who is singing in the classroom? listen some birds are singing in the tree 填空:Listen!Many()are singing in the tree. Listen!Who is singing in the next room?这里为什么要用singing bird the in singing tree is a 连词成句 a bird is singing in the old tree The bird in the tree is singing.划线部分提问 in the tree 是划线部分 Listen!Helen is singing in the next room. 单项选择 listen!the bird ------- now. A :is singing B:sing C:san