A number of students ______ playing on the ground but I don't know what the exact number______.

The important sports festival, the Olympic Games,        held every          years.

These increased harvests _____ that 22% of the world’s people are fed from just 7% of the farmland in China.

Every boy and every girl ______ that each day and each hour brings ______ duty.

 The sign on the right tells us taking photos ________here.