In the last 100 years, which of the following have added excess carbon dioxide to the atmosphere?
a. power plants
b. machinery
c. cars
d. all of the above

The correct answer option D

Carbon emission have increased in the last 100 years because of many ways. The excess of carbon dioxide in the environment is caused due to the following reasons.

The power plants, machinery and the cars combinely releases carbon dioxide and many more harmful gases that contributes in increasing the level of carbon in atmosphere.