Which of the following statements about scientists' views of global warming is true?

a.) nearly all scientists agree that the earth's temperature is rising and that humans are responsible.
b.) nearly all scientists agree that the earth's temperature is rising, but many disagree about whether humans are responsible.
c.) nearly all scientists agree that the earth's temperature is rising, but most agree that humans are not responsible.
d.) there is no consensus among scientists on this issue; they disagree over whether the earth's temperature is rising.