利用江河湖海水库等天然水源作为消防水源时，其设计枯水流量保证率宜为（）。

A．80％～85％ 

B．80％～90％ 

C．90％～95％ 

D．90％～97％

Which of the following would not be an indication of placental detachment

A．An abrupt lengthening of the cord.

B．An increase in the number of contractions.

C．Relaxation of the uterus.

D．Increased vaginal bleeding.