第2题: [单项选择]假设某股票一个月后的股价增长率服从均值为2%、方差为0.01%的正态分布，则一个月后该股票的股价增长率落在( )区间内的概率约为68%。 A. [1%，3%] B. [0，4%] C. [1.99%，2.01%] D. [1.98%，2.02%] 参考答案:A 答案解析:[解析] 方差为0.01%，则标准差为1%。正态随机变量x落在距均值1倍标准差范围内的概率为P(μ-σ＜X＜μ+σ)≈68%。因此，区间为[2%-1%，2%+1%]即[1%，3%]。
第19题: [单项选择]切除巨大血管瘤时，为减少术中出血，术前最好采用（）。 A. 小剂量放疗 B. 颈外动脉结扎 C. 反复多次冷冻 D. 反复多次YAG激光气化 E. 超选择性供血动脉栓塞术 参考答案:E
第20题: [单项选择]Questions 19 to 22 are based on the passage you have just heard. A. They chased the bear away. B. They stayed outside the tent and did nothing. C. They climbed up a tree. D. They put some honey outside for the bear to eat. 参考答案:B 答案解析:[解析] Q: What did they do when they saw a bear enter their tent
