Which of the following is least likely a disadvantage of a callable bond to an investor The:（）

A. investor is exposed to reinvestment rate risk.

B. cash flow pattern of a callable bond is not known with certainty.

C. issue often offers a higher coupon rate than a comparable option-free bond.

人体平衡反应的形成时间有一定的规律，通常在()

A．2～3个月形成俯卧位平衡反应 

B．4～6个月形成仰卧位和坐位反应 

C．7～8个月形成蹲起反应 

D．9～11个月形成爬行反应 

E．12～21个月形成站立反应