NO.PZ2018122701000068
问题如下：
Jack Ma, FRM, is studying difference model, including mean-reverting models, no-drift models, models that incorporate drift, and Ho-Lee models. Ma makes the following statements about the appropriate usage of these models:
Statement 1: Both Model 1 (no drift) and the Vasicek model assume non-parallel shifts from changes in the short-term rate.
Statement 2: The Vasicek model implies decreasing volatility in short-term rates while Model 1 assumes constant volatility of future short-term rates.
Statement 3: The Model 2 (constant drift model) is a more flexible model than the Ho-Lee model.
How many of the statements is/are incorrect?
选项：
A.0
B.1
C.2
D.3
解释：
C is correct.
考点：Term structure models
解析：要求选错误的陈述有几个。
Statement 1不正确. Model 1 assume parallel shifts from changes in the short-term rate.
Statement 2 正确.
Statement 3不正确.The Ho-Lee model is actually more general than Model 2, as no drift and constant drift models are special cases of the Ho-Lee model.
因此，有2个陈述错了，答案选C。
1.Statement 2说σ会变小。但是 关于V-model，σ不是不变的吗，constant。为什么这里说它是对的呢
2.提问也有人问了，但是我看老师说，"这里的voatility不是指公式中的σ，而是收益率曲线的standard deviation。"但是这句话我不理解，因为公式中的σ本来不就是说的rate的波动率吗，这不是一个东西吗，那一会说恒定，一会说变小，怎么理解
