问题如下：
Wang, a fixed-income portfolio manager, manages a fixed-income portfolio in a wealth management firm. The portfolio is in a laddered structure with maturities ranging from 1-year to 30-year and the duration of the portfolio equals to that of the benchmark at the moment. The duration of the portfolio is allowed to fluctuate ±0.5 from its benchmark duration. Wang plans to sell the bonds at all maturities except the 2-year and 30-year and use the proceeds to invest in 2-year and 30-year bonds. By using the appropriate weights, Wang leaves the portfolio duration unchanged before and after this strategy. According to Wang’s strategy, he is most likely to expect the yield curve will:
选项：
A.The yield curve will experience a downward parallel shift.
B.The yield curve will become more flattening
C.The yield curve will become more steepening
解释：
B is correct.
考点：考察不同收益率曲线变动情况下，对应的策略
解析：Wang只是在整个portfolio的Structure做了调整，并没有调整整个Portfolio的Duration大小，因此排除A选项，否则应该增加整个portfolio的duration来享受收益率曲线向下平移带来的好处。因为Wang卖出了其他所有期限的债券，只留下了2年期、30年期的债券，因为Wang认为留住这两个期限可以受益。30年期利率下降可受益，这种情况对应的是Yield curve flattening，因此B正确。
老师，这道题我觉得A不能选还有一个原因是，A没有说是small还是large平移，如果是large parallel就要结合convexity了呀，而barbell的convexity大，在这种情况下是可以获得超额收益的吧？
