In Lesson 5, assignment 22, two of the self-check answers are wrong.
Exercise 3
Number 5 - the question reads: "Adolescent is certainly far from a uniformly pleasant period." The answer reads: "Adolescence is certainly a far from a uniformly pleasant period. Correct."
Number 7 - the question reads: "Of middle age, the best that can be said is that a middle-aged person has likely learned how to have a little fun in spite of his troubles." The answer reads exactly the same, but is not shown as correct.
These are small mistakes, but to someone who has never learned this before could be very confusing.