_________ English can be difficult to learn, it is a very useful tool for communication.
| A．As | B．When |
| C．While | D．Because |
31. The Tower of London is _____ the Church tower.
| A．twice high than | B．two times as high as |
| C．twice higher as | D．three times the height of |
You can hardly imagine the difficulty the woman had _____ her children.
| A．taking up | B．turning up | C．bringing up | D．pulling up |
Our class is made up of 54 students, _____ are girls.
| A．of which two-fifths | B．of whom two-fifths |
| C．two-fifth of which | D．two-fifth of whom |
It is the prevention of disease______its successful treatment that has led to the rapid increase of the world’s population.
| A．rather than | B．less than | C．in addition to | D．in the direction of |
They looked forward with hope _____ from you, but you never wrote a word to them.
| A．of hearing | B．to hear | C．to hearing | D．hearing |