An Astronomer Is Observing a Distant Galaxy Which Looks Blue

Multiple Choice

An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?

A) the galaxy must be moving toward us (must have a blue shift)
B) the galaxy must be extremely large (probably a giant elliptical)
C) the galaxy must have a lot of star formation going on at the time we are seeing it
D) the galaxy must be rotating very slowly or not at all
E) the galaxy must contain only older stars (those that formed billions of years ago)