Currently, many American women are still faced with the ________ of choosing between work and family commitments.

A successful scientist needs _____ if he wants to make hypothesis (假设) of how processes work and how events take place.

Thanks is a common _____ used in English. You can never use it too much.

----What do you know the _____ of are the pig influenza in humans? ---- usually similar to regular human seasonal influenza .

The short-answer test is a kind of____between the composition and  selection types.