Question

it has been estimated that the

英语语法
1.it has been estimated that if the bridge were packed with cars ,it would still only be carrying a third of its total capacity.
2.i asked a passenger if this was the westhaven express,but he had not even heard of it.
第一句话中是不是可以理解为一个同位语从句（那如果以逗号分开的话那就是一个句子有两句话了那是不是不行的?
第二句话那个是不是要分开理解的,if this was the westhaven express是宾语,那个but he had not even heard of it又是另外一句话呢?

Answer 1

1.句子的主干是it has been estimated,其中it是作形式主语,而真正的主语是that if the bridge were packed with cars ,it would still only be carrying a third of its total capacity这个主语从句.
只有名词才会有同位语（且名词和它的同位语通常是放在一起的）,同位语是指表达同一事物的句子成分,可以理解为同位语是来进一步解释说明这个名词的.而这个句子的主干中是没有名词的,所以该从句不是同位语从句.
其次这是一个从句套从句的句子,从句的第一层应当是that （if the bridge were packed with cars ,）it would still only be carrying a third of its total capacity,而括号中由if引导的从句是主语从句中的条件状语从句.
如果你将逗号前后看作两个句子那就涉及到两方面的错误：
a.两个单独的完整的句子之间是不可以用逗号的,必须用句号.除非两个句子之间有并列连词才能使用逗号.
b.从逻辑含义上看句意也是不对的,如果将第一句话分为it has been estimated that if the bridge were packed with cars,那么它的句意都是不完整的(if在此表“如果”).
2.but是并列连词（but是表转折关系的并列连词）,在此它前后连接的是两个完整的句子（因为有并列连词所以两个完整的句子之间可以用逗号隔开）.而对于第一个句子,它的语法结构是ask sb.sth.,if引导的宾语从句就是占据了sth.的位置（这里if表“是否”）.
（我的语法分析是很强的,如果你采纳我的回答的话能帮忙提高一下悬赏的财富值吗?因为我现在差财富值来提问,如果不勉强的话就提高一下吧,我会非常感谢的!如果不行,也没有关系）