In a given population where an allele frequency shifts by random chance, the evolutionary process at work is most likely:.a. mutation b. selection c. genetic drift d. gene flow

genetic drift

Explanation:

hope this helps

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

b. lithosphere, asthenosphere, mesosphere   is the answer most likely