Exercise 2, page 38 Listen the attachment and complete the gaps with the correct missing words.

Have you 1) wondered how mountains are formed? If you know about volcanoes, you know a little bit already. The Earth's crust is made 2) of over 50 tectonic plates that push and pull to form mountains; and this happens so slowly that we don't even notice it. The wind, rain and ice also cause mountains to change shape. There are several types of mountains, so let's take a closer look at the three most common ones.