Okay, let's underline the correct verbs in each sentence:
1. They always pick/rake flowers in May.
*Explanation:* In this context, 'pick' is more suitable as flowers are typically picked rather than raked.
2. They sometimes play/go in the snow, don't they?
*Explanation:* 'Play' makes more sense here as it describes an activity done in the snow.
3. They usually shine/rake leaves in the autumn.
*Explanation:* 'Rake' is the correct verb here because leaves are raked.
4. They always go/play swimming in the summer.
*Explanation:* 'Go' is the correct verb to use before swimming.
5. It's warm and the sun is shining/raking.
*Explanation:* The sun 'shines'.
6. It's raining greatly/heavily now.
*Explanation:* 'Heavily' is more commonly used to describe how it's raining.
7. It's swimming/freezing today, isn't it?
*Explanation:* 'Freezing' is the appropriate verb here to describe the weather.
8. It's very cold/hot today. We can go swimming.
*Explanation:* It cannot be "cold" and people can go swimming. "Hot" it the word that matches the sentence context.