重点讲解：
1. at a time 一次；每次；
He was able to spend only a few days at a time on the island.
他每次去岛上都只能呆几天k.Oro@T0GAYV@AU-SrGV。
2. acquainted with 了解的；熟悉的；
He was well acquainted with the literature of France, Germany and Holland.
他对于法国、德国和荷兰的文学了如指掌;G#EDWF.N_])VXAl。
3. ward off 避开，躲开，防止(危险、疾病等)；
Mass burials are now under way in an effort to ward off an outbreak of cholera.
为防止霍乱爆发正在进行大规模掩埋g*fo2&B|mX.pO。
4. be rich in 富含…的；含有大量…的；
Oranges are rich in vitamin C.
橘子含有丰富的维生素C.LS&XhZuCVVcIt。