Why is natural selection often referred to as “survival of the fittest?

What is the difference between an igneous, sedimentary and metamorphic rock

Cedric has a low fever and minor aches. yesterday, he went to the doctor for his booster shot and receive the flu shot. which best explains why he has this reaction?

What are the two causes of density in deep current waters? a. salinity (how much salt) of the water and high temperaturesb. salinity (how much salt) of the water and low temperatures c. oxygen content of the water and high temperatures. d. oxygen content of the water and low temperatures