Even a Little First-Grader Can Stay Up on a Bicycle

Multiple Choice

Even a little first-grader can stay up on a bicycle if he can get his bicycle moving fast enough because

A) the angular momentum of the wheels wants to stay horizontal, due to conservation of angular momentum.
B) the first-grader's weight causes a torque too small to make the bicycle fall sideways when moving.
C) pedaling faster is easier once you are stable, and more pedaling increases net angular momentum.
D) All of these.