In order for a massive star to form a black hole, it must first
a. expand
b. emit x-rays
c. run out of fuel
d. begin rotating faster

Genetic diversity is the variation in the genes of an entire species. each circle represents a population of a particular species in different habitats. select the population with maximum genetic diversity

How can scientists test their ideas about the origin of the universe if they can't physically interact with or study?

Match the following terms describing electrical events with the correct phases of the cardiac cycle. the ventricular muscle cells depolarize at the start of this phase. during this phase, na+ entry through the funny channels causes the pacemaker potential of sa nodal cells to gradually become less negative until it reaches threshold. the ventricular muscle cells repolarize right before this phase. the cytosolic concentration of calcium in the contractile cells of the ventricle is highest during this phase. a. isovolumetric relaxation b. ventricular ejection c. isovolumetric contraction d. ventricular filling