We can never expect bluer sky unless we create less polluted world.

Every driver is _____ to obey the traffic rules.

is known to all is that the Diaoyu Islands have belonged to China since ancient times.

I am afraid to ask questions because of my poor ______.—You’d better practice speaking more.

Every year, a great many visitors come to visit the temple ____ the 12th century, ______ has brought a large income.