The answer is A.
Prokaryotic organisms are simpler than eukaryotic organisms are are single-celled. They do not contain the genetic information to form complex, specialized structures as eukaryotes do, so they cannot form multi-cellular bodies. The remaining options apply to both prokaryotes and eukaryotes.
The answer is B, or They can survive in changing salinity.
You can draw a free body diagram with two 250N forces acting on the human, one from each side. The net force is 0 because the two applied forces cancel each other out since they are in opposite directions.