注意事项：
　　(1)在非正式场合， that有时可用来代替关系副词或相当于关系副词的“介词+which”，而且经常全部省略，
　　如：In all the years that (=when/during which) I was at collage
　　在我读大学的那些年里
　　the reason that(=why/for which)he is not happy
　　他不高兴的理由
　　The direction(that)(=in which )the heavenly bodies move can’t be changed.
　　天体运行的方向是不可改变的。
　　He is unpopular because people don’t like the offensive way (that)(=in which) he talks.
　　他不受欢迎的原因是他说话的方式让人讨厌。
　　(2)是用关系代词还是用关系副词：
　　关系词(包括关系代词和关系副词)是学习英语定语从句的关键。用关系代词还是用关系副词，一要看关系词在从句当中作什么成分;二要看关系词所代表的是人、物、时间、地点还是原因;三要看所引导的是限定性定语从句还是非限定性定语从句。所以同样的先行词会有不同的关系词，这是因为关系词在从句当中担当的作用不同而决定的。
　　如：This is the room where/in which we’ll celebrate the New Year.
　　这是我们将要在里面庆贺新年的房间。(充当地点状语)
　　This is the room(that /which)we’ll celebrate the New Year in.
　　这是我们将要在里面庆贺新年的房间。(充当介词宾语，可省略。)
　　This is the room which /that will be used for the celebration of the New Year.
　　这是那个将要被用来庆贺新年的房间。(充当主语)
　　This is the room (which/that) we’ll use for the New Year dinner party.
　　这是我们将要用来举行新年晚宴的房间。(充当宾语，可省略。)
　　The reason (that /which) he had given was not sound enough.
　　他给的理由不够充分。(充当宾语，可省略)
　　The reason why/for which he had done that was not sound enough.
　　他做那件事的理由不够充分。(充当原因状语)
　　This is the house where she lives.这是她住的房子。
　　【比较：This is the house (that/which) she has bought. 这是她买的房子。This is the house that/which I’ve told you is extremely expensive.这就是我和你说过极其昂贵的那幢房子。】
　　I met him in the year when I was first in Xi’an.
　　我刚到西安的那年遇到了他。
　　That is the reason why he did not come that morning.
　　那就是那天上午他没来的原因。
　　(3)定语从句中的时态。如果主句是一般将来时或过去将来时，从句的动作与主句的同时发生，那么该从句要用一般现在时表示一般将来时、用一般过去时表示过去将来时。
　　例：Anyone who/that touches the wire will get an electric shock.
　　任何碰这根电线的人将受到电击。(不用will touch)
　　I would give her anything that she asked for.