a. Diagonal line illusion: many poses have diagonal lines especially along legs, arms and backs. Strategy - hold up a pencil, use plumb lines, simplify diagonals and add subtler curves after.
b. Illusion - long lines, we tend to scan across easier than up and down and we are effected by the end of lines. Strategy - find as many reference points as possible and take measurements.
c. Illusion - circle with more space seems to be smaller but they are the same. . Strategy - read the negative space around the objects.

d. Is the left center circle bigger than the right center circle? No, they are both the same size.
e. Which is the longer A-B or B-C? They are both the same.

f. In life drawing we tend to rely on lines more heavily than needed. Try and imply line when there is no tonal difference between a divide.

g. Is the book pointing towards you or away from you? It depends on your point of view. In your drawing it is often hard to tell how much foreshortening is occurring the best solution is to move to a different viewpoint and see.
h. We are so accustomed to seeing closure that we sometimes close things that aren't. When we are drawing form unusual angles occasionally extra information needs to be added to counteract our asumptions.
i. We tend to group objects with similar properties (color, shape, texture). Folds and complicated shapes can become even more confusing because of the way we group things. Look at the big simplified areas of the drawing and add the detail later.