Mandela met a lot of difficulties, he still fought for the equal rights of his people.

You _____ be 18 years old before you are allowed to drive a car ,and it’s also essential to get a driver’s license

It was on May 12, 2008 ______ the Wenchuan Earthquake happened.

People cut down too many trees, _____ the greenhouseeffect becomes more and more serious.

Teenagerstheir health because they play computer games too much