Why should galaxy collisions have been more common in the past than they are today?

a. galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars.

b. galaxies were much bigger in the past since they had not contracted completely.

c. galaxies were closer together in the past because the universe was smaller.

d. galaxies were more active in the past and therefore would have collided with each other more frequently.

Use the table to answer question 22 23 and 24.

Asubject in a clinical research trial experiences a serious, unanticipated adverse drug experience. how should the investigator proceed, with respect to the irb, after the discovery of the adverse event occurrence? a. do not report the adverse drug experience to the irb since it is a common adverse experience. b. report the adverse drug experience to the irb only if there are several other occurrences. c. report the adverse drug experience as part of the continuing review report. d. report the adverse drug experience in a timely manner, in keeping with the irb's policies and procedures, using the forms or the mechanism provided by the irb.

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.