Please keep the secret to ________, children! Don’t let anybody else know it.
Jack likes to sit ________ the back of the bus.
---- What are you doing?---- I’m ________ my English book.
I borrow a book from my friend and I can ________ it for a week.
---- ________ class are you having? ---- Math.
I don’t like physics ______ it’s too difficult for me.