阅读下面短文。从短文后所给的A、B、C三个选项中选出最佳选项。

    A man stopped at a gas station and bought a soft drink. He stood by his car to 1 and he watched a couple of men 2 along the roadside.

    One man would dig a hole two or three feet 3 and then move on. 4man came along behind to fill in the hole. While one was digging a new hole, the other was about 25 feet behind 5 in the old hole.

    The man with a soft drink was confused. "I can't stand this," said the man walking toward the men. "Stop it," he said to t e men. "Can you tell me what's 6 here?"

    "Well, we work for the county government," one of the men said.

    "But one of you is digging a hole and the other is filling 7up. You're not accomplishing anything. Aren't you 8 the county's money?"

    "You don't understand," one of the men said.

    "Normally (通常地) there are 9 of us: I Rodney and Mike. I dig the hole Rodney sticks in the tree and Mike here puts earth 10."

    "Yeah," said Mike. "Today Rodney is sick. But that doesn't mean we can't work, does it?"

下列城市中被誉为“日光城”的是（     ）

54的 $\frac{2}{3}$ 相当于90的多少？

观察下列算式，你发现了什么规律？

1²= $\frac{1\times 2\times 3}{6}$ ；1²+2²= $\frac{2\times 3\times 5}{6}$ ；1²+2²+3²= $\frac{3\times 4\times 7}{6}$ ；1²+2²+3²+4²= $\frac{4\times 5\times 9}{6}$ ；…

①根据你发现的规律，计算下面算式的值；1²+2²+3²+4²+5²=____；

②请用一个含n的算式表示这个规律：1²+2²+3²…+n²=____；

③根据你发现的规律，计算下面算式的值：51²+52²+…+99²+100²=____．