中国在19世纪上半期出现了“千古未有之变局”，政治上的独立自主、经济上的自给自足现状被打破，开始沦为半殖民地半封建社会。这种“变局”开始于（    ）

    It is Saturday morning. The sky is blue. My father and I are going to the park. There are a lot of people in the park. Some children are running on the grass. A dog is running after them. Some men are sitting on the grass. They are talking. Two girls are flying a nice kite. Three women are standing under a tree, and they are watching the children playing. There is a boat in the lake and two women are boating. Everyone in the park is very happy.