A locomotive (engine) pulls a series of wagons. Which is the correct analysis of the situation?

The train moves forward because the locomotive pulls forward slightly harder on the wagons than the wagons pull backward on the locomotive.

Because action always equals reaction, the locomotive cannot pull the wagons. The wagons pull backward just as hard as the locomotive pulls forward, there is no motion.

The locomotive's force on the wagons is as strong as the force of the wagons on the locomotive, but the frictional force on the locomotive is forward and large while the backward frictional force on the wagons is small.

The locomotive can pull the wagons forward only if it weighs more than the wagons.