All of the following are characteristics of benign tumors except
a. they do not spread.
b. can sometimes be present as cysts.
c. cannot increase in size.
d. cause problems only when they become large enough to interfere with the normal functioning of neighboring organs.
e. are considered noncancerous.

THE threat of Yellowstone erupting in the future and the sheer size of the supervolcano means Yellowstone is the most dangerous natural cataclysm on Earth, a geologist has warned. Yellowstone volcano's last three major eruptions occurred 640,000, 1.3 million and 2.1 million years ago respectively.