China is a country with the largest population in the world,          we all know it.

 _____ you have offered 50 yuan , you can telephone for 100 yuan.

______ there is a snowstorm or other bad weather ,the bus always comes on time.

All the photographs in this book,     stated otherwise, date from the 1950s.

(2013·北京，26)—What do you think of teaching，Bob?—I find it fun and challenging.It is a job ________ you are doing something serious but interesting.