2、从句、表语从句、宾语从句和同位语从句四种类型。其引导词的选用主要有以下几种情况:(一)若从句陈述某一事实或情况,则引导词在从句中就不做任何成分而只起引导从句的作用,其引导词就用that,如: 1.That he had met a kind policeman in this city gave us no surprise. 2.Word came that the students would put off the outing until next wee
3、k, when they wouldn’t be busy. 在这类名词性从句中,引导词that 在主语从句、表语从句和同位语从句中不可省略,而在宾语从句中有时可以省略,但如果是两个以上的宾语从句并列出现,则that在第二个及以后的从句中绝对不能省略,此外,介词except和in后的宾语从句引导词that不可省略。例如: I know (that) she was born in the countryside and that she came here to look f
4、or a job.另外,除了except和in以外,介词后一般不跟that引导的宾语从句。 (二)若从句表示疑问、怀疑或不了解情况,且引导词不在句中作任何成分,引导词就用if或whether,意为“是否”,一般情况下二者可以互相替换,但在下列情形中只能用whether而不能用if。 1.当主语从句出现在句首时; 2.在表语从句、同位语从句及介词后的宾语从句中; 3.宾语从句的后半部分出现“…or…”表示选择时; 例如:Whether
5、she is coming on time still remains a problem. (三)若从句表示疑问、怀疑或不知道,而引导词在从句中担任某种成分,那么我们就要根据引导词的语法成分和词义来选用一些疑问词作引导词。具体而言,引导词在从句中指人作主语就用who,作宾语用whom,作定语用whose;指物作主语、宾语或表语用what,作状语用when、where、how等。例如: 1.The word media basically refers to what
6、 we usually call newspapers, magazines, radios and TV. 2.You’d better choose whoever is kind and friendly to help you. 在这类从句中,如果要表达“无论……”的含义时,从句引导词只能用wh.-ever而不能用“no matter wh.-”这种结构。例如: 1.Whatever I said wouldn’t make you bel
7、ieve me. 2.You can choose whenever you would like to come. reason (原因)后面的同位语从句引导词只能用why,他做主语时,其表语从句的引导词用that。例如: The reason why he quarreled with his wife is that she cares him too much. 二、定语从句定语从句属形容词性从句,常用来修饰限制名词、名词短语或整个句子所
8、描述的情况,其引导词一般都在句子中担任某种语法成分。对于这种引导词我们可以根据其所指代的对象及其在从句中所担任的句子成分来进行选择。主要有以下几种情况: 1.引导词指代人在从句中作主语用who或that, 作宾语用whom,还可以省略; 2.引导词指代物在从中作主语或宾语用that或which,作宾语时还可以省略。如果从句的先行词是不定代词、序数词或形容词最高级,或者被序数词、形容词最高级或受Theonly,the very ,any ,few,li