Part 1 of the assignment
For this picture, I used a long focal length.Which means that it is a telephoto lens. Professional photographs use often this kind of lens to do portraits as people will seems have a better appearance with that kind of lens.
For this picture I used a short focal length which means that will give wide angle lens. As you can see, the person of this picture seems to have a wider more and a deformed face. This is why this lens is not usually used for portraits.
Part 2 of the Assignment
I used shade setting for this picture making the colors nicer as it made a longer exposure.
For this picture, I used tungsten setting which made the picture's color more blue.
Part 3 of the assignment
The colors of the skin of the girl on that picture are prettier because her face takes most of the picture as their is not a lot of space left for the background and for light on the picture. The camera tries to make the picture more clear be by putting the color lighter to make mid-grey as the camera always want to obtain mid-grey.
Oppositely to the last picture, the camera want to make mid-grey by doing the opposite. As the picture has more light colors the camera will try to make the picture darker in order to obtain mid-grey.