You can only be sure of _______ you have at present; you cannot be sure of something _______ you might get in the future.

Why did your father get ______ with you just now— Because I did even ______ in the writingcompetition this time.

Haven’t seen you for ages! Where have you been—I went to Ningxia and there for one year, teaching as a volunteer.

It is these poisonous products ______can cause the symptom of the flu, such as the headache and aching muscles.

My English teacher is very ______ because he always explains problems over and over again.