To them is optional in 1&2. Anonymous he doesn't understand the answer and wants the instructor to explain it once more. "It" is optional here.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
Anonymous he doesn't understand the answer and wants the instructor to explain it once more."It" is optional here. "To explain" can be transitive or intransitive. It doesn't necessarily require an object.