5 The great fish moved silently through the night water, propelled by short sweeps of its crescent tail. The mouth was open just enough to permit a rush of water over the gills. There was little other motion: an occasional correction of the apparently aimless course by the slight raising or lowering of a pectoral fin—as a bird changes direction by dipping one wing and lifting the other. 6 The eyes were sightless in the black, and the other senses transmitted nothing extraordinary to the small, primitive brain. The fish might have been asleep, save for the movement dictated by countless millions of years of instinctive continuity: lacking the flotation bladder common to other fish and the fluttering flaps to push oxygen-bearing water through its gills, it survived only by moving. Once stopped, it would sink to the bottom and die of anoxia.

A. People should learn more about sharks and their past.
B. Historically sharks are at the top of the food chain and will stay there.
C. Modern sharks have come a long way and will continue to evolve.
D. Even though sharks are seen as dangerous, they need our help.
E. Due to evolution, sharks have become the most intelligent species.
F. Sharks may not be able to evolve quickly enough to survive with humankind.