The CAS9 enzyme does each of the following except:

a. destroy the host dna

b. cut DNA and add new pieces

c. carries the viral genetic code

d. recognizes viral DNA

i think it's c

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.