The tree diagram below shows all of the outcomes for flipping 3 coins.

A tree diagram has outcomes (H, H, H), x, (H, T, H), (H, T, T), (T, H, H), (T, H, T), (T, T, H), (T, T, T).

Which outcome is represented by x?
heads on the first coin, heads on the second coin, and tails on the third coin
heads on the first coin, tails on the second coin, and tails on the third coin
heads on the first coin, heads on the second coin, and heads on the third coin
heads on the first coin, tails on the second coin, and heads on the third coin