---Must I go to the gym three times a week? ---No, you ______. Twice a week is OK.
—Have your read the article A Dirty Beijing, which is about air pollution?—Yes. It’s highly informative. I _____no idea that the PM2.5 there sometimes reached 300.
—What do you think of being a volunteer, John?—I find it a stressful job but one ___ you can really help people.
—Is there anything wrong, Bob? You look sad.—Oh, nothing much. In fact , I ____ of my friends back home.
It is not always easy for the general public to see _____use a new invention can be of to their daily life.
More highways have been built in China, ______ it much easier for people to travel from one place to another.