The ____ of AIDS has led to an expansion in research seeking a cure.

单选题

The ____ of AIDS has led to an expansion in research seeking a cure.

答案解析

单选题

18. The ____ problem of bringing a spaceship back from the moon has been solved.

答案解析

单选题

The government has received many reports about the threat of the disease over the ____ few months.

答案解析

多选题

Britain has the highest ____ of road traffic in the world -- over sixty cars for every mile of road.

答案解析

单选题

The doctor has saved a lot of lives ____ he became a doctor.

答案解析