In general, yes, the dorsal blood vessel of a worm be seen from the worm's exterior because a worm's "skin" is very thin. Although of course there are exceptions.
Pretty sure it's D, hope I helped
The neuron releases chemical messengers. Otherwise, there would be no 'signal transduction' in the postsynaptic cell. So, your answer is B.
Answer:
Estimates of historical world population
Year 1400 1600
population (in billions) 0.35–0.40 0.50–0.58
growth p.a. >0% 0.15–0.3%
