重点讲解：
1. leave behind 留下；余留；
The criminal didn't leave behind any traces of his crime.
罪犯没有留下任何作案的痕迹!Vd7QE+UIw!Z6d5GS。
2. at the expense of 以牺牲…的利益为代价；
But skeptics worry that costs may be trimmed at the expense of the patient.
但是持怀疑态度的人担心费用的削减会以牺牲病人的利益为代价t2nS)D|jhY。
3. take over 接管，控制；
A British newspaper says British Airways plan to take over Trans World Airways.
一家英国报纸称，英国航空公司计划接管环球航空公司[AHMOOi9I+Q-Uw.(BF。
4. prop up 支撑；维持；
Investments in the U.S. money market have propped up the American dollar.
对美国资金市场的投资扶持了美元F)I@HymEREixuT=。