对于羊水，不恰当的是（）

A.妊娠早期的羊水是母血清经胎膜进入羊膜腔的透析液

B.妊娠中期以后主要来自胎儿尿液

C.羊水的吸收50％由胎膜来完成

D.母体与羊水的交换，主要通过胎盘，每小时约3600ml

E.妊娠足月时羊水比重1.007～1.025

Vijay Ranjin, CFA, is a portfolio manager with Golson Investment Group. He manages a fixed-coupon bond portfolio with a face value of $ 120. 75 million and a current market value of $116. 46 million. Golson’s economics department has forecast that interest rates are going to change by 50 basis points. Based on this forecast, Ranjin estimates that the portfolio’s value will increase by $2. 12 million if interest rates fall and will decrease by $2.07 million if interest rates rise. Which of the following choices is closest to the portfolio’s effective duration（）

A. 3.6.

B. 0.4.

C. 2.9.