用所给介词填空（答案要告诉我为什么这样做）

用所给介词填空（答案要告诉我为什么这样做）
by in at on with to under for
They like swimming_______the sea.
I wrote a letter________my friend in Australia.
Tom's birthdayis_______Jamuary.
The National Day is_______Friday.
He read the book_______himself.
Last Sunday morning,I played basketball_______my friend Tim.
It is rainy today.My sister is unhappy.I sing a song_____her.
Do you often go to school_______bus or_______foot?
They are singing and dancing______the trees.
Bill is staying________home because he is hill.