reached是謂語,后面必須接賓語,所以用what引導(dǎo)賓語從句而where引導(dǎo)的是狀語從句,前面必須要有一個(gè)地點(diǎn).比如,He reachedwhat was oncehis home.He reached his home where he once lived there....Do you know where he lives 為什么可以用where,這個(gè)也是賓語從句前面沒地點(diǎn)啊He reachedwhat was oncehis home。用what 的原因是，它既是reached的賓語，又是 后半句的主語，相當(dāng)于漢語中的兼語成分。英語中只有what有這個(gè)用法。Do you know where he lives 。中where的確是引導(dǎo)一個(gè)賓語從句。這兩者并不矛盾的。