— Listen! Is that Linda singing in the next room?— No, it ________ be her. She is still in Shanghai.
You should _______ the doctor’s advice and _______ the medicine on time.
_______ necessary for us _______ our environment clean and tidy.
She was afraid of __________SARS because it was dangerous.
-----Who taught _________Japanese? ----I learned it by ______________.
Humans can’t live _______air.