选择缓冲溶液时，应使其（）。
A.酸性或碱性不能太强
B.所控制的pH值在缓冲范围之内
C.有足够的缓冲容量
D.对分析过程无干扰
参考答案：B, C, D
根据《中 * * 党机关公文处理条例》规定，下列不属于党的机关公文的是( )。
A．指示
B．通报
C．批示
D．决议
On 1 January, Hellen’s portfolio is valued at $1000000. Hellen want to make a $100000 payment to buy a house on 31 December of the same year, but does not want the year-end portfolio value to fall below $1000000. The expected annual return on the investor’s existing portfolio is 15 percent with an expected standards deviation of 20 percent. The risk-free rate is 8%. The safety-first ratio for the portfolio is closest to:（）
A. 0.10.
B. 0.25.
C. 0.35.
