They are singing and dancing...(in,on,under) the trees:选词填空

under符合逻辑

是 under the tree 在树下

on the tree 是指长在树上的 比如
树上有些苹果。——There are some apples on the tree.
in the tree 是外来的东西在树上。
比如；树上有只猫。
There is a cat in the tree.

They are singing and dancing under the trees.
他们在树下唱歌跳舞。

under
in 是指在、、里
on 是指在、、上面
under是指在、、的下面（有一定空间）

UNDER!