Question

SAT OC语法！！

A recent discovery is the finding that people who both dreink and smoke are greater cancer risks than those who do only of these things.
A. It has recently been discovered that
B.it is a recent discovery that
为什么选A？OC答案说B中的it多余，为什么？

Answer 1

A recent discovery is the finding that people who both dreink and smoke are greater cancer risks than those who do only of these things.
中是drink ，不是dreink吧！A recent discovery是主语， is为系动词 ，the finding 是表语，that people who both dreink and smoke are greater cancer risks than those who do only of these things是finding的同位语．此句为主系表结构的句子．

让我们写完整来看
A.
It has recently been discovered 　that people who both dreink and smoke are greater cancer risks than those who do only of these things .
它的主动语态形式是people who both dreink and smoke are greater cancer risks than those who do only of these things　has recently been discovered .但是这样会显得头重脚轻，看起来很费尽，也容易引起语法问题．
A句中，It是形式主语，that引导的从句作真正的主语． has been discovered 是谓语．是一个主谓句．
B.
It is a recent discovery　 that people who both dreink and smoke are greater cancer risks than those who do only of these things.
it不是多余的，仍然是形式主语，不同的是：that引导的从句作discovery的同位语．是一个主系表结构的句子．

根据语法来看，都是正确的，只是A更适合而已．B句很不地道，像一些报导性的文章里，是不会用B句的．