在1.5亿年前的沉积物中发现了已经灭绝的剑尾动物，对每个个体背甲的长宽之比都进行了测量，这一比值用S表示。在下图中，P曲线表示1.5亿年前该动物S值的分布。在1亿年前的沉积物中，在三个不同地点发现了三个不同剑尾动物的群体。图中a、b、c分别表示三种动物群体中S值的分布情况。请据图回答下列问题：
要形成新物种必须经过（）、（）、（）三个环节。
参考答案：突变；自然选择；隔离
| The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth. By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist. Once the sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the earth, it will become a white dwarf star. The sun may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf. After billions of years as a white dwarf, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the earth will be dark and cold. If any atmosphere remains there, it will have frozen onto the earth’s surface. |
The word "fueled" underlined in Paragraph 1 most probably means ______ .
A．powered
B．bombarded
C．created
D．pushed