根据语境，填入适当的词语或句子，补全对话。

A: How dirty your clothes are! What did you do today?

B: We planted trees just now.

A: Oh, I         1          it's Tree Planting Day today. Where did you work?

B: At the foot of the hill.

A:          2           ?

B: The one behind our school.

A: How did you get there?

B: On foot. It's not         3         our school, you know.

A: But what made your clothes so dirty?

B: I        4        the river when I was carrying water.

A: Bad luck. You'd better go to see a doctor.

B:          5          . Only my shoes are wet through.