The correct answer is (2)
The moon's rotational period was wasn't always equal to its orbit (revolution) around the planet. Just like gravity of the moon affects ocean tides on the earth, gravity from earth affects the moon. But because the moon lacks an ocean, earth pulls on its crust, creating a tidal bulge at the line that points toward earth.
Gravity from earth pulls on the closest tidal bulge, trying to keep it aligned. This creates tidal friction that slows the moon's rotation. Over time, the rotation was slowed enough that the moon's orbit and orbit and rotation matched, and the same face became tidally locked forever pointed toward earth.
