《南京条约》签订后，中国的茶叶、生丝等农产品出口量大量增加，导致这一现象的根源是

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   Betty is an American school girl. She is very happy because her parents will take her to China for a visit. They are going to fly from New York on June 30 and get to Beijing on July 1. They will stay at Lido Holiday Inn. Their Chinese friends will show them around Beijing. They are going to visit the Palace Museum, the Summer Palace, the Temple of Heaven and the Great Wall. They will also visit some Chinese homes and try some Chinese food. They will spend a week in Beijing and then go to Xi’an, Guilin and some other places for sightseeing. The whole trip will take three weeks and she is sure she will have a great time in China.

“（蒋）介石先生······领导全国各民族进行空前伟大的民族革命战争，凡我国人无不敬仰······***谨启。民国二十七年九月二十九日。”，这封信的直接背景是