(2013·合肥一中二模)The school recommends parents ________ their children to swim in rivers or lakes during summer holidays.

A．not permit

B．do not permit

C．mustn't permit

D．couldn't permit

出于对消费者剩余和企业利润分配公正的考虑，政府定价的规范理论通常给出了定价的预算约束，即（）。

A．成本约束

B．收入约束

C．利润约束

D．收支约束