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.
