Which of the following statements about the greenhouse effect is true?

A. Life on earth is suffering because of the greenhouse effect.
B. All greenhouse gases are harmful.
C. Life on earth would not exist without the greenhouse effect.
D the greenhouse effect is caused by human activity.

A

Explanation

Its not b because not all greenhouse gases are harmful

Its not c because life on earth would be better without it

its not d because we contribute to the cause of the greenhouse effect but we do not cause it

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.