-19.SMALL WHALES
Dolphins and porpoises, often called simply "small whales," are mammals, not fish, and are thus warm-blooded, keeping their body temperature nearly constant even when they are exposed to different environmental temperatures. The mothers provide milk for the young for a year or more. Like other whales, dolphins have lungs and breathe through a single nostril, called the blowhole, located on top of the head. The blowhole is opened during their frequent trips to the surface to breathe. In contrast to some of the large whales, dolphins and porpoises have teeth, which they use to seize their food, consisting primarily of marine fish. Certain species of marine dolphins are the best-known biologically because they survive well in captivity, which means they can be more carefully observed. The bottle-nosed dolphin has been the most intensively studied because of its adaptability to salt-water holding tanks. It is a major participant in acrobatic shows at oceanariums and is noted for its curiosity toward humans.
One of the differences between some whales and dolphins is that, ------ .
whales don't provide milk for their young, but dolphins do
although dolphins have lungs for breathing, most whales don't
while all dolphins are warm-blooded , whales are cold-blooded
whales are less aggressive than dolphins and not as big as them
whereas all dolphins have teeth, some whales don't have any
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