周末，爸爸和妈妈带洋洋去离家12千米远的游乐园玩，他们从家门口坐出租车去游乐园，根据规定，出租车起步价为5元（3千米以内），超过3千米部分，平均每千米按l.5元收取，到了游乐园，爸爸应给出租车司机多少元呢？

It ________ have been her to leave her child alone and do whatever she wanted. She isn't such a person.

A．couldn't　

B．mustn't

C．mightn't　

D．wouldn't