The correct answer is: act.
The other options are not as appropriate because they do not convey the urgency of the situation. To stop pollution, we need to take action now. We cannot afford to wait any longer. We need to act decisively and with a sense of urgency.
Option A: act. This is the most appropriate answer because it conveys the urgency of the situation. We need to take action now to stop pollution. We cannot afford to wait any longer.
Option B: operate. This option is not as appropriate because it does not convey the urgency of the situation. We need to take action, not just operate.
Option C: behave. This option is not as appropriate because it does not convey the urgency of the situation. We need to take action, not just behave.
Option D: perform. This option is not as appropriate because it does not convey the urgency of the situation. We need to take action, not just perform.
In conclusion, the correct answer is: act.