Here are the best words for each sentence in Exercise 1:

1. I don't like hotels. I prefer staying on a **c. campsite**.
2. I always go to school on a **b. foot**.
3. There isn't any rain here. We have a lot of **a. droughts**.
4. I hate the sea, so I never travel by **a. ship**.
5. I can't see much. It's very **b. windy** today.
6. My mum loves **b. sightseeing**. She always visits museums on holiday.

For Exercise 2, here are the matches from column A to column B:

1. solar - **f. power**
2. green - **g. apartment**
3. global - **e. warming**
4. pedal - **b. skates**
5. recycled - **d. paper**
6. inline - **a. boat**

For Exercise 3, the completed sentences are:

1. Do you usually choose products with little **packaging**?
2. Do you recycle your **r**?
3. I often go to the seaside. I love sitting on the **beach** and relaxing in the sun.
4. **Pollution** is a big problem in my city. We've got a lot of traffic and very bad air.
5. We'll probably have heavy rain and **showers** tomorrow in the morning.

For Exercise 4, the sentences can be completed as follows:

Robert has got three **younger** sisters: Kate, Gina and Maria. Kate studies a lot and she's the **best** (good) student in her class. She is also the **most intelligent** (intelligent) than her sisters. Gina is very kind - in fact, she's a **nicer** (nice) person I know.