—What does PM 2.5 mean?—It's a professional ________ indicating the condition of air pollution.
Fitness is important in sport, but of at least _____ importance are skills.
It's usually warm in my hometown in March, but it ___ be rather cold sometimes.
I have _____ all my papers but I still can't find my notes.
—Now that you like computers very much, isn't that a good idea to get a ____? —Well, I'd like to, but I can't afford such an expensive computer at present.
I have many friends, ____ some are businessmen.