根据所给句子和首字母提示写出恰当的单词，每空一词。When she was 20 months old, she learned to look after h____________.
I don’t want anybody else to know the thing. Please keep it s__________.
He is fat now but he only weighed 2.5 kilos at b__________.
________（polite），he drove the old man out of the room and shouted at him angrily．
Be careful to cross the street when we meet heavy________（traffic）．
My mother can’t sleep well，and sometimes she even stays________（wake）the whole night．
Is it possible for us human beings to leave all the animals in the________ ________（自然环境）？
Some of my friends are interested in________ ________（集邮）．