| Value | Category | Cases | |
|---|---|---|---|
| 1 | Gases in the atmosphere that trap heat | 1666 |
20.3%
|
| 2 | The Earth's protective ozone layer | 545 |
6.6%
|
| 3 | Pollution that causes acid rain | 1641 |
20%
|
| 4 | How plants grow | 1469 |
17.9%
|
| 98 | Don't know | 0 |
0%
|
| c | 2902 |
35.3%
|