I know the answer is C already. I thought it was B and C but B was wrong and C was right can you explain why B is not right and why C is right? also can you explain why A and D is incorrect too? (I would also prefer if you typed it out on keyboard).

For the alphabet = {a, b}, give regular expression for the language of all strings that contain the substring ab.

A. ab(a + b)*

B. (a + b)*ab

C. (a + b)*ab(a + b)*

D. ab(a + b)*ab