Figure 1 shows a parallel beam of monochromatic green light traveling in water. The beam approaches the flat, horizontal upper surface of a rectangular flint glass block at an angle. Below the glass block is a layer of air, separated from the glass by a parallel horizontal boundary.

CD is a wavefront of the green light.
Discuss the propagation, speed, and direction of the wavefront CD as it enters the flint glass block from the water, and then subsequently leaves the block to enter the air.