In my opinion, the key ____air pollution is to inspire people to take public transport in big cities.

s to his pension, Li Zhentian, _____ give each of his grandchildren RMB 5 as a Chinese New year gift for the first time.

__, Mark Twain became worldwide famous at once [ ]

rdered some pizza, so we _______ worry about cooking when we get home tired.

Where are you going on vacation this summer, Australia or America— Australia. Because the weather in Australia is cooler than _________ in America.