一个句子中只能有一个动词不是完整的说法, 应该是一个句子中可以有多个随主语的人称, 数, 和时态变化的谓语动词, 如: He gets up, brushes up, has breakfast at around 7a.m. during weekdays. 其他不随主语人称, 数, 和时态变化的动词是非谓语动词 :

如 : He leaves home early every Sunday to catch a train. 这里的leaves 必须随主语的人称, 数, 和时态变化-- 第一人称 : I leave, 过去时 : He left, 但to catch则不随主语的人称, 数, 和时态变化, 它就是非谓语动词.

Need to do st. 这里的need 是实义动词, 必须随主语的人称, 数, 和时态变化, 如 :He needs to do the cleaning everyday. We need to do the cleaning everyday. to do 就是非谓语动词.

另外, need 同时也是情态动词, 后面直接跟实义动词 : You need do the cleaning everyday. need 作情态动词时的否定是: needn't, 如, You needn't do the cleaning everyday.. 而need 作实义动词时的否定是don't/doesn't need to do: 如: You don't need to do the cleaning everyday.