阅读下面这篇短文，短文后有2项测试任务：(1)第23～26题要求从所给的6个选项中为规定段每段选择1个正确的小标题；(2)第27～30题要求从所给的6个选项中选择4个正确选项，分别完成每个句子。
As early as kindergarten we’ re taught that there are nine
planets, but 200 years ago, even scholars were sure there were only six
planets. 2. As recently as the 1700s, people still believed
that the planet Saturn was at the farthest extent of the solar system. That
there might be other planet wasn’t even a respectable idea. 3.
In 1781 a self-taught astronomer, William Herschel, was "sweeping the skies"
with his telescope. By March, he had reached the section including the
constellation Gemini, and he spotted an object that appeared as a disk rather
than a glowing star. Because it moved slightly from week to week, Herschel
thought it was a comet. After a few mouths, however, he decided the orbit was
circular’" and came to the shocking conclusion that it wasn’t a comet, but an
unknown planet. 4. People were astonished. No one since ancient
times had anyone named a planet. Herschel felt that is should be called
"Georgium Sirius" (George’s Star) after George Ⅲ, the king of England, some
wanted to name it "Herschel" after its discoverer. But one influential
astronomer suggested "Uranus", after the Greek god of the heavens. That made
sense, since it was thought to be the limit of the solar system. 5.
Could there be another planet affecting Uranus A century earlier, Isaac
Newton had come up with laws describing the effects that the gravitational
forces of planets have on one another. Using Newton’s laws, two young
scientists, Jean Leverrier and John Couch Adams set out independently in 1840 to
find the unknown planet whose gravitational forces might be pulling on Uranus.
Both hoped the unknown planet would be where their calculations said they could
find it. Adams finished his calculations first, in September 1845. The following
August, Leverrier completed his. 6. Leverrier traveled to the
Berlin Observatory in Germany, and the young assistant mana get, Johann
Gottfried Galle, agreed to help search for the planet. That was September 23,
1846. That night, Galle looked through the telescope, calling out stars and
their positions while a young student astronomer, Heinrich Louis d’ Arrest,
looked at a star chart, searching for the stars Galle described. Finally Galle
called out an eighth-magnitude star that d’ Arrest couldn’t locate on the
charts. They had found the unknown planet! It had taken two years of
research—but only a half hour at the telescope. The honor of the discovery
belongs to both Adams and Leverrier, who had essentially discovered the new
planet with just a pen and a new set of mathematical laws. The greenish planet
was named after Neptune, god of the sea. The effect of a planet’s orbit may be due to______.A. after each of these planets