When it _____ air pollution, Beijing faces the 3 “C” s: cars, coal and construction, which lead to Beijing’sserious air pollution.

er asked to help me with mylessons, he always refuses, ______ he is too busy.

This is ____ useful book.And ____ book is____.

It was strange that he _____ have utteredsuch rude remarks on that occasion

Jimmy is ________ late for his grandma’s birthday, is he