必须, 不得不

他必须立即走。

自然的，母猪提供了液体奶，并且营养高，但是断奶后，小猪则需要自己区分饥饿和口渴，同时要它们自己通过不同的器具满足饥渴需求。

情势所迫，只好如此。

community periodontal index for treatment needs, CPITN

basic human needs

human needs

hierarchy of needs

equality and mutual benefit and mutually supplying each other's needs【贸易】

needs

hierarchical theory of needs

meet the needs of