名词性从句及不定式、动名词作主语时，谓语动词一般用单数形式。【例如】To finish the work in advance is what he wants.Smoking cigarettes is dangerous to your healthWhat seems easy in theory is difficult in practice.What caused the accident is a complete mystery.但是，what引导名词从句作主语时，其表语是复数形式时，系动词也可以是复数形式。【例如】What we badly need here are qualified teachers.
连系动词基本用法连系动词是表示不完全谓语关系的动词，它与其后的表语一起构成谓语。常见的连系动词有be(是)，become(成为)，get(变成)，remain(还是)，seem(似乎是)，look(看上去)，feel(感觉)等。连系动词后的表语通常是名词和形容词，有时也可以是代词、数词、副词、介词短语、不定式、动名词、从句等：His English is excellent. 他的英语很棒。(跟形容词)Money isn’t everything．金钱不是一切。(跟代词)She was the first to arrive．她是个到达的人。(跟数词)Who is upstairs? 谁在楼上？(跟副词)He is with his friends. 他和朋友在一起。(跟介词短语)He seems to be ill. 他似乎病了。(跟不定式)Seeing is believing. 眼见为实。(跟动名词) </p 产品：澳博培训供货总量：不限产品价格：议定包装规格：不限物流说明：货运及物流交货说明：按订单
