Seeing their teacher ________ into the classroom,they stopped ________ at once.
I’m sorry I’m late again________ the heavy rain.
If it_________ tomorrow, I’ll go birdwatching with my father.-----That’s a good idea.
Not everyone knows_____they want to be.
Science is _____ difficult for some students ____ learn, so many of them don’t like it.
---What are you doing?---I’m_____my English book.