50.（ ） both sides accept the agreement（ ）a lasting peace be established in this region.

80.Our experiment was conducted under （optimal） conditions. The underlined part means（ ）.

79.The employers prepared, with all due（ ）for a conference with the Trade Unions.

78.There is no （conceivable） reason why there should be any difficulty during the project. The underlined part can be replaced by all the following EXCEPT（ ）.

77.The whole country was in（ ）over the result of the elections.

76.His mother retired early （on account of） poor health. The underlined part means（ ）.

75.The flags in the stadium（ ）in the wind.

74.Our school did not（ ）for Christmas until mid-December.

73.He （turned his back on） them when they most needed him. The underlined part means（ ）.

72.The chief of surgery became committee chairman by virtue of（ ）.

71.The family of the victim had to （endure） a long wait before the case cane to trial. The underlined part means（ ）.