61. on the average(=on average，on an average)平均

62.(be)aware of(=be conscious of，having knowledge or consciousness)意识到，知道

63. at the back of(=behind)在…后面

64. in the back of 在…后部(里面);on the back of 在…后部(外面);be on one's back(=be ill in bed)卧病不起.

65. at one's back(=supporting or favoring sb.)支持，维护;have sb. at one's back有…支持，有…作后台