Answer the following question given this paragraph: 

Surface waves travel along the ground outward from an earthquake’s epicenter. Surface waves are the slowest of all seismic waves. They travel at 2.5 km (1.5 miles) per second. There are two types of surface waves. Love waves move side-to-side, much like a snake. Rayleigh waves produce a rolling motion as they move up and backward ( Figure above ). Surface waves cause objects to fall and rise. They also cause objects to sway back and forth. These motions cause damage to rigid structures during an earthquake.


Q: How many types of surface waves are there?

 Choices:

- over a hundred

- three

- six

- two

A:
two
