1. a couple of 两三个，几个

　　Although he thought of the key idea in 1951， the first maser was not completed until a couple of years later.

　　2. account for 解释

　　Variations of clay composition and the temperatures at which they are fired account for the differences in texture and appearance.

　　3. adapt to 使适应于

　　They have been able to adapt to ecological changes.

　　4， adorn with sth 用…装饰

　　Some pots were adorned with incised or stamped decorations.

　　5.appeal to 吸引

　　Publishing literature consisting of exciting stories that would appeal to both children and adults

　　6.apply to 适用于

　　Ethological theory began to be applied to research on children in the 1960’s.

　　7.at best 充其量，最多

　　Hunting is at best a precarious way of procuring food， even when the diet is supplemented with seeds and fruits.

　　8.at intervals 相隔一定距离

　　However， at intervals of 10 to 100 years， these glaciers move forward up to 100 times faster than usual.

　　9.at the expense of sth 在损害…的情况下

　　A multitude of microorganisms make their livings directly at the expense of other creatures.

　　10.at the height of sth 在…最鼎盛时期

　　The violin had reached the height of its popularity by the middle of the eighteenth century.

　　11.back and forth 来回地

　　They then spiral back and forth between the Earth's magnetic poles very rapidly.

　　12.be absent from 缺席，不在

　　Lacking the right to vote and absent from the seats of power， women line were not considered an important force in history.

　　13.be capable of 能…的

　　Many animals are capable of using objects in the natural environment as rudimentary tools.