Which sentence has correct capitalization?

Josh was taking a U.s. history class, and he loved reading about the U.s. Constitution.
Josh was taking a u.s. history class, and he loved reading about the u.s. Constitution.
Josh was taking a U.S. history class, and he loved reading about the U.S. Constitution.
Josh was taking a U.S. history class, and he loved reading about the u.s. Constitution.

Question

Which sentence has correct capitalization?

    Josh was taking a U.s. history class, and he loved reading about the U.s. Constitution.   
    Josh was taking a u.s. history class, and he loved reading about the u.s. Constitution.  
    Josh was taking a U.S. history class, and he loved reading about the U.S. Constitution.
    Josh was taking a U.S. history class, and he loved reading about the u.s. Constitution.

logan13 · Answer

not a test

anonymous · Answer

the third one

eclipsedstar · Answer

Hi there @myGODisawesome0613 ! Did you know that giving direct answers is against the CoC? Please read it here: http://openstudy.com/code-of-conduct . Thank you for your consideration. :D

anonymous · Answer

oh im sorry it wont happen again:(