It is （very）likely that从句：（很）可能……；……(很)可能
it 是形式主语，that 从句为真正的主语。比较：
It is likely that he will go.= That he will go is likely.可能他会走。
又如：
It’s very likely that she’ll dance tonight. 很可能今晚她跳舞。
=That she’ll dance tonight is very likely. 很可能今晚她跳舞。
It is likely that the school will have to close. 这家学校可能要关闭。
= That the school will have to close is likely. 这家学校可能要关闭。
It's more than likely that the thieves don't know how much it is worth.
盗贼很可能不知道此物的价值。（more than= very）
It's likely someone gave her a lift, or else that she took a taxi.
可能有人开车捎了她一程，要不就是她打了辆出租车。
《柯林斯高阶英汉双解学习词典》
知识拓展：
as likely as not=most/very likely很可能
As likely as not she's forgotten all about it.
她很可能把这事忘得一干二净了。
