Water is the cheapest drink. And it is also ______.
—Whose workbook is this, Tony?—Look! Ann's name is on it! It ______ be hers.
—______ will you come back from Shanghai? —In one month.
—I went to Daming Lake yesterday. There were ______ people.—Yes. Everyone wants to go out on such a good day.
More and more people find ______ necessary to protect our earth.
My father has ______ for two weeks. I miss him so much.