强调句可以强调形容词吗？比如It was clear that

不可以，这个很明显是it作为形式主语的句型，再如

it is important that we should learn English well.
强调句型It is(was)...that分别可以强调主语、宾语、地点状语和时间状语。如：
It was he who(that)read three books in the library yesterday.
(强调主语)
It was three books that he read in the library yesterday.(强调宾语)
It was in the library that he read three books yesterday. (强调时间状语)
当被强调部分指人时，可用that，也可用who；指物时，只用that, 如：
It was Tom who(that)I met last week.
It is a new bike that his brother wants to buy.
一般来说，判断一个句子是不是强调句型就是把it is（was）...that这三个单词去掉，如果句子还是完整的话就是强调句型，如上面的例句都来自于
He read three books in the library yesterday. 只是分别强调的部分不一样