为慢性菌痢病人作保留灌肠，正确的是()。

A．在晚间睡眠前灌入

B．灌肠时取右侧卧位

C．肛管插入7～10cm

D．液面距肛门40cm

E．灌肠宜保留20～30分钟

Under perfect competition, the short-run market supply curve is most accurately described by which of the following statements The market short-run supply curve is the:（）

A. average of the quantities at each price along the marginal cost curve for all firms in a given industry.

B. sum of the quantities at each price along the average total cost curve for all firms in a given industry.

C. sum of the quantities at each price along the marginal cost curves for all firms in a given industry.