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

66. turn one's back on sb.（=turn away from sb. in an impolite way）不理睬（某人），背弃，抛弃

67. behind one's back背着某人（说坏话）

68. be based on / upon基于

69. on the basis of根据…，在…基础上

70. beat…at在…运动项目上打赢

71. begin with以…开始to begin with（=first of all）首先，第一（经常用于开始语）

72. on behalf of（=as the representative of）以…名义

73. believe in（=have faith or trust in；consider sth./sb. to be true）相信，依赖，信仰

74. benefit（from）受益，得到好处

75. for the benefit of为了…的利益（好处）