When the teacher ______ how to do the experiment, the bell rang.
—Would you mind opening the window? —____. Look at the heavy haze (霾) outside.
It’s ____ useful book. And ____ book is popular with students.
—Is your headache getting _______? —No, it’s worse.
—Which is your new neighbor, Liu Hua? —The man _______ T-shirt is red.
—Do you know _______ the Capital Museum? —Next Friday.