Genetic counselors typically receive a bachelor's degree in biology, social science or a related field, and then go on to receive specialized training, so I would say your answer would be B.) must have a degree in biology or genetics. I hope this helps!
Extinct is correct. When no members of a species remain, the species is said to be extinct.
plants get nitrogen from ammonium and nitrate
The answer is vitamin D. This is actually a group of vitamins of similar molecular structure responsible for facilitating increased absorption of calcium, magnesium and phosphate from the gut. The most important of the vitamin D compounds are vitamin D3 and D2. While vitamin D can be obtained from your diet and supplements, the major source of vitamin D is from a chemical reaction dependent on skin exposure to the sun.