The passage that uses verb tenses consistently is:
The game of chess is complex. Alexander, who takes lessons from his uncle, can’t always remember how each piece is supposed to move on the board.
This passage uses the present tense consistently: "is" (present tense) for the game of chess, and "takes" and "can’t" (both present tense) for Alexander. The phrase "is supposed to move" also uses the present tense.