选择题：中国近代历史的起点标志是?A、虎门销烟B、鸦片战争C、洋务运动D、中华民国建立

设M是实数集，代数运算是普通加法，下列映射是M的自同构的是选项A:x→x2B:x→sin xC:D:

The reason（）we were unable to reach a decision is that everybody has his or her

Every single person here has the （）to learn and succeed, and I need only look ac

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假定∮是A与间的一一映射，a∈A，则∮-1{∮（a）}和∮{∮-1（a）分别为选项A:a，aB:无意义，C:无意义，无意义D:a，无意义