1. With the development of economy, our income has increased _______ 10% in less than a year.

A. by               B. for              C. on               D. at

2. The professor could tell by the  ___________look in Maria’s eyes that she didn't understand a single word of his lecture

A. cold             B. blank            C. innocent             D. fresh

3. Vehicle accidents have claimed many deaths in the past few years. _______ more action is taken, the problem will get dramatically worse.

A. Unless               B. If                  C. After                D. When