不要误用which替代强调结构中的that
根据英语强调结构的基本格式it is (was)…that (who)…可知，不管被强调成分为指时间或地点，还是指原因或方式等，其后一律要用that，不可用when, where, why, how等。至于其中的who，它只用于被强调成分指人的场合。如：
他是昨天晚上才第一次亲她。
误：It was last night when he kissed her for the first time.
正：It was last night that he kissed her for the first time.
我昨天是由于想买本字典而进城的。
误：It was because I wanted to buy a dictionary why I went to town yesterday.
正：It was because I wanted to buy a dictionary that I went to town yesterday.