Which two of the following are main ideas of the article?
1. carbon shifts from one area to others through the slow and fast carbon cycles.
2. when the ocean takes in more carbon than it releases, it becomes more acidic.
3. rain breaks down rocks, which are eventually brought to the ocean.
4. human behavior has led to increased carbon levels in the atmosphere.
question 3 options:

1 and 2

1 and 4

2 and 3

3 and 4