1．(2012·安徽，29)A lot of language learning, ________ has been discovered, is happening in the first year of life, so parents should talk much to their children during that period.
A．as B．it
C．which D．this
答案：A as和which都可以引导非限制性定语从句，代表整个主句或者主句的部分内容。as意为“正如，正像”，位置比较灵活，位于主句的前面、中间或者主句的后面都可以；which意为“这件事”，一般位于主句的后面。句意：正如被发现的一样，大量的语言学习发生在生命的头一年，因此在那个阶段父母应该多和孩子交流，由句意可知，A项符合题意。
2．(2012·北京，26)When deeply absorbed in work, ________ he often was，he would forget all about eating or sleeping.
A．that B．which
C．where D．when
答案：B which引导非限制性定语从句，且在从句中作表语，代替整个主句的内容。句意：“通常情况下，当他沉浸在工作中时，他会忘了吃饭和睡觉。”
3．(2012·福建，23)The air quality in the city, ________ is shown in the report, has improved over the past two months.
A．that B．it
C．as D．what
