In spring, it is good for you to sleep ________your windows open.
The river is very deep. My mother warns me _________ in it.
She hardly ever speaks English because she is afraid ________ mistakes _______grammar.
I don’t know ______ he will be back ______ the Dragon Boat Festival.
---Have they finished ________ the Water Festival? ---No, they haven’t.
---Excuse me. Do you know these English words? ---Sorry, I don’t. But you can __________ in a dictionary.