What are you doing, John? Why stop?—To be on the safe side, we’d fill up the car now for we _______ run out of gas on the way.
At present, lots of people would rather ________ in the country because there is ________ pollution in the city.
_______ do you help the old man with the housework —Once a week.
You shouldn’t drive fastIt’s dangerous
geles Times reported that researchers may have found a way to ______ human life by changing certain genes, so that humans might expect to live twice as long.