桑代克的准备律与现代学习心理学中的（）相一致。

A．动机原理

B．强化原理

C．学习的发展准备原理

D．成熟概念

Each of the integers from 0 to 9, inclusive, is written on a separate slip of blank paper and the ten slips are dropped into a hat. If the slips are then drawn one at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10 ？（）

A．Three

B．Four

C．Five

D．Six

E．Seven