B.<em>to gain support for a law that would improve student achievement</em>
Explanation:
This excerpt from a speech by US secretary of education Arne Duncan makes many references to secretary's purpose of speech i.e. gaining support for a law. These references are; "replace it with a law that..." , "A law that recognizes that no family..." , "A law that recognizes the critically hard" and some others. So, option A and C cannot be correct.
