Which is a mark of a galaxy formed by collapse?(1 point)

uniformly young stars

same age stars

abundant gas and dust

a mix of young and old stars

The Milky Way has changed course to head toward Andromeda.

All galaxies will collide at some point.

The two galaxies have collided previously.

Astronomers have observed their movements over time.

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

The graph shows the amount of global warming happening in different ecosystems. which populations of organisms will likely decline the most as a result of climate change, and why? a.coral reefs because of the loss of the symbiotic algae living within their bodies b.penguin populations because the fish they eat will move into warmer waters c.mountain-dwelling birds because rising sea levels will relocate their food sources d.large cats in the rainforest because of decreased habitat loss for their prey

Natural selection changes allele frequencies because some survive and reproduce more successfully than others.