是作”宾语”，还是作”状语”？
What is learned in the cradle is carried to the grave.
其中，to the grave是作”宾语”，还是作”状语”？
参考答案:是补语(Complement)。
准确的说，是主语补语。因为这个句子使用了被动语态，原来的宾语(即What ...cradle 这个从句)变成主语。
楼上说是宾语的理由很可笑，谓语后面一定是宾语吗？
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Complement
Grammar a word, phrase, or clause governed by a verb that completes the meaning of the predicate. ▶an adjective or noun that has the same reference as either the subject or object (as "mad" in "he is mad" or "he drove her mad").
参考资料：Concise Oxford English Dictionary