They were so far away that I couldn’t _____ their faces clearly.

What is upsetting you, dear—________ it is necessary for us to move our home to the city.

Science is really _______ useful sucject although it is very difficult.

It’s crazy of you to spend more timeplaying computer games than you ______ studying.

your uncle take a taxi to the airport．Why didn’t you drive him there—I,but my car．