Which of the Following Describes a Major Danger of Interstellar

Multiple Choice

Which of the following describes a major danger of interstellar travel at near-light speed?

A) Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays.
B) Any interstellar journey will take much longer than the lives of the crew members.
C) Time dilation will slow the heart beats of the crew to a dangerously low rate.
D) Asteroid fields floating in interstellar space will present a navigational challenge.