Figure shows behavior of a wavefront when it passes through a prism.

Which of the following statement(s) is/are correct?
I) Lower portion of wave front (B’) is delayed resulting in a tilt.
II) Time taken by light to reach A’ from A id equal to the time taken to reach B' from B.
III) Speed of wave front is same ever where.
IV) A particle on wave front A’B’ is in phase with a particle on wave front AB.