Complete the sentences with correct relative pronouns.

1. Planet Earth, _______ is also called the Blue Planet, is covered with water and land.

2. Peter Molnar, _______ has done many studies on climate change, is one of the best-known Earth scientists.

3. Neil Armstrong, _______ trip to the moon marked a giant leap for mankind, was the first to walk on the moon.

4. Suoi Thau, _______ is in Ha Giang, is one of the most gorgeous grasslands in Viet Nam.

5. People often do green things to protect Earth on the Earth Day, _______ is celebrated on 22nd April.