补全对话。
A:                                 last Sunday?
B: Yes, I did. My classmates and I went to plant trees.
A: How did you plant trees?
B: First, we                   in the ground. Then, we
                     and put them into the holes.
After that, we                      . We watered the young trees.
A:                                ?
B:  Yes, they are. They can stop the wind and they can make the air fresh and clean.
A: We should plant more trees.
Are the trees very important to people?
we brought young trees.
Did you go to plant trees
we used spades to dig holes
got water from the river nearby.