閱讀短文，并根據(jù)所給的句首單詞用完整的句子回答問題。
?Mr Green is a doctor.He often goes to work on foot.One day Mrs Green gave him a letter and asked him to mail（郵寄）it.When he walked along the street，a man came up from behind him and smiled."Don't forget （忘記）to mail that letter！"he said. Then a girl walked by and said it，too. Mr Green felt strange.At last he came to a mailbox and mailed it.But again a man asked "Did you mail your letter？" "Yes."said Mr Green. "Then I can take this off，" said the man.There was a paper on Mr Green's back（后背）and it said "Ask him to mail the letter".
（1）What does Mr Green do？
He

is a doctor.

is a doctor.

（2）How does Mr Green go to work？
He

often goes to work on foot.

often goes to work on foot.

（3）What did Mrs Green ask Mr Green to do？
She

asked him to mail a letter.

asked him to mail a letter.

（4）短文畫線句子中的"it"指代的是什么？（抄出具體指代的內(nèi)容）
" It " refers to（指的是）

"Don't forget to mail that letter！"

"Don't forget to mail that letter！"

（5）How did the people know that Mr.Green had a letter to mail？
Because

there was a paper on Mr Green's back and it says "Ask him to mail the letter".

there was a paper on Mr Green's back and it says "Ask him to mail the letter".