With more and more farmers moving to cities, an inadequate labor force is    becoming a major factor affecting the country's grain output.

It has been proved that taking exercise ________ does good to one’s health. 

________，the search engine just gave me some brief introductions rather than the whole content of the book to read.

The city of Jilin is beautiful all the year around,         in winter. The Jilin rime attracts plenty of tourists.

-He seems to be doing nothing, but    he is just waiting for his chance.