If the carbon dioxide levels (choose one: increase/decrease/stay the same), then the average global temperatures will (choose one: increase/decrease/stay the same)
over time.

1. increase

2. increase

If the carbon dioxide levels increase, global temperatures will increase, because carbon dioxide is a greenhouse gas.

If I chose stay the same, this is what would happen:

If the carbon dioxide levels stay the same, global temperatures will stay the same because not too much or less carbon dioxide is being emitted to the atmosphere.

If I chose decrease, this is what would happen:

If the carbon dioxide levels decrease, global temperatures will decrease because there will be less greenhouse gases to make the atmosphere warmer.

Hope this helped you!

iii. and iv. only is the right answer