One of the main causes of air pollution in cities is emissions from vehicles like cars and trucks. Cars emit various pollutants which are bad for human health when inhaled, like 1. Nitrogen oxides $\left(\mathrm{NO}_{\mathrm{x}}\right)$ 2. Carbon monoxide (CO) 3. Carbon dioxide $\left(\mathrm{CO}_2\right)$. 4. Benzone Which of the above pollutants are not tolerated by human beings even at very low levels?

• A

  1 and 4 only
• B

  1 and 2 only
• C

  1, 2 and 3 only
• Correct answer
  D

  1, 2 and 4 only

Hence, the correct answer is option: 'D'.