Students sometimes support themselves by _______ of part- time jobs.

Listen! Is that Linda singing in the nextroom— No, it ________ be her. She is still in Shanghai.

If his parents are convinced ______ the fact that his son always focuses his mind _______his study

下列各句没有语病的一项是

Rising evidence suggests that the use of the vaccines(疫苗)will be effective tothe spread of common cold.