On average, how often does a six-meter diameter asteroid collide with Earth?
a. once a year
b. once every five years
c. once every ten years
d. once every fifty years
e. once every century
Question 2
NASA catalogs near-Earth-objects (NEOs) that are larger than ____ in diameter and come within about 75 million km of Earth.
a. 10 m
b. 100 m
c. 1 km
d. 5 km
e. 15 km