1.what do many scientists believe contributed to the extinction of the dinosaurs
a. asteroid impact b. global warming c. predators d. plate tectonics

2.which of the following may lead to the breakdown of the ozone layer in the stratosphere a. carbon dioxide b. methane c. oxygen d. chlorofluorocarbons

3. which of the following statements about the greenhouse effect is true
a. all greenhouse gases are harmful b. life on earth is suffering because of the greenhouse effect c. life on earth would not exist without the greenhouse effect d. the greenhouse effect is caused by human activity