Combine the two sentences into one, using a non-defining relative clause.

1. The Moon is Earth's only natural satellite. Its surface is dark.

2. Moonquakes are much weaker than Earthquakes. Moonquakes can last up to half an hour.

3. Mars has mountains and canyons on its surface. It is a rocky planet like Earth.

4. Venus is considered the twin sister of Earth. Venus has a similar size and structure as Earth.

5. We should protect rivers and lakes. Rivers and lakes provide humans with their main sources of fresh water.