PLEASE HELP ME!! A dam is built across a river to generate electricity. What is likely effect of the construction of a dam on the river?

a)increase in the size of fish in the river
b)increase in the water flow in the river
c)decrease in the population of aquatic organisms in the river
d)decrease in the amount of pollutants dumped into the river

Up until 1938, paleontologists accepted the idea that coelacanths (an ancient fish) went extinct at the time that they last appear in the fossil record, about 80 million years ago. but in 1938, a live coelacanth was discovered off the coast of south africa that was compared to the fossil record and found to be the same species what goal of science does this discovery represent