如果你没有奖励积分，廉价航空公司则是第二最优之选。
If you do not have reward points, budget airlines are the next best bet.
第二个积分比第一个积分更易于接近。
The second integral is easier to approximate than the first one.
第二类换元法是一种既重要又不易掌握的积分方法。
The second method of transformation is an important but not-easy-to-master calculus method.
第二部分，国内外高中微积分教学的现状分析。
The second part: Domestic and foreign high school calculus teaching present situation analysis.
第二部分，国内外高中微积分教学的现状分析。
The second part: Domestic and foreign high school calculus teaching present situation analysis.
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