Within the last two and a half billion years, how many snowball Earth events have occurred?
A) zero
B) one
C) two
D) four
Question 2
Two spaceships are traveling through space at velocities of 0.600c and 0.900c, respectively, with respect to Earth. If they are headed directly toward each other, what is their approach velocity, as measured by the captain of either ship?
What will be an ideal response?