定語從句是由關(guān)系代詞或關(guān)系副詞引導(dǎo)的從句，其作用是作定語修飾主句的某個(gè)名詞性成分，相當(dāng)于形容詞，所以又稱為形容詞性從句，一般緊跟在它所修飾的先行詞后面。
（1）When television was first introduced, the extent to which it could affect human society could not have been foreseen.
人們發(fā)明電視的時(shí)候，并沒能預(yù)見到它會(huì)對(duì)人類社會(huì)產(chǎn)生多大的影響。
（2）As is so often pointed out, knowledge is a two-edged weapon which can be used equally for good or evil.
正如人們常常指出的，知識(shí)是一把雙刃劍，既可以用于造福，也同樣可以用來為害。
定語從句按照關(guān)系代詞的不同，會(huì)有不同的情況。
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