A whale is a mammal, and it breathes through its lungs. So once in a while _____ to the top of the water for air.

Bat<br/>is to mammal as ( )<br/>()boar<br/>is to hog A: porpoise<br/>is to shark B: butterfly<br/>is to insect C: whale<br/>is to fish D: reptile<br/>is to lizard E: boar is to hog

Which of the following is an opinion? A: The average fox weighs 14 pounds. B: The bat is the only mammal that can fly. C: A lion in the wild usually makes no more than twenty kills a year. D: Birds are not fun to watch.

定义一个哺乳动物 Mammal类，再由此派生出狗 Dog类，二者都定义 Speak() 成员函数，基类中定义为虚函数，定义一个Dog类的对象，调用 Speak函数，观察运行结果。

It’s not known whether chronic stress will harm the narwhals, but researchers are concerned. “The results are disturbing because they suggest narwhals aren’t physiologically equipped to sustain, in good health, repeated exposure to stressful events,” says Randall Reeves, a marine mammal expert in Hudson, Canada, who chairs the International Union for Conservation of Nature Species Survival Commission’s Cetacean Specialist Group. “It makes me worry that narwhals are even more specialized than was previously thought, and that they