重点讲解：
1. by comparison
与…相比；与…比较而言；
eg. This one costs more but is cheaper by comparison.
这个价钱贵一点，但是比较起来还是便宜的。
eg. By comparison, this house has the advantage of low price and that house has the advantage of convenient transportation.
相比较起来，这幢房子的优点是价格低，而那幢房子的优点是交通便利。
2. at risk
处境危险；有风险的；在危险中；
eg. The disease is spreading, and all young children are at risk.
疾病正在流行，所有的幼儿都有危险。
eg. The whole future of the company is at risk.
公司的整个前途受到威胁。
3. contribute to
促成；促使；是导致…的原因之一；
eg. Fatigue contributed to his defeat.
疲劳导致他的失败。
eg. His gambling contributed to his downfall.
他的败落与他的赌博不无关系。
