阅读下列短文，从每题所给的四个选项（A、B、C、和D）中，选出最佳选项，并在答题卡上将该项涂黑。

　　Located in Pisa, the Leaning Tower of Pisa in Italy has become the sign of Italy. It is the third oldest structure in Pisa's Cathedral Square. There are eight floors in the Leaning Tower of Pisa including observation deck at the top. The weight of the tower is about 14,500 metric tons. There are amazing facts of the Leaning Tower of Pisa that we will mention here.

　　The Leaning Tower of Pisa was not originally intended to lean, but because it was built on soft soils the tower gradually leaned to one side. Prior to its restoration (修复) from 1990 to 2001, the tower had a tilt (倾斜) of 5.5 degrees. Many people think that it will fall one day. Millions of tourists come to the lawns around the tower to take the classic photo pretending to hold up or knock down the tower.

　　It is said that you must visit the Leaning Tower of Pisa during the day. At night the shops are closed and it appears unimpressive. But, if you plan to visit on a full moon night, the tower will look charming. Mornings are the best time to beat the crowds. Summer in Pisa is very hot and wet, but you can expect rain in fall and winter.

　　Even though some people regard the tower to be an engineering failure owing to the tilt, the tower has acquired a special place in history. The tower has also been used for experiments by the famous Italian scientist named Galileo Galilei. He is believed to have thrown two balls of different mass from the tower to prove that their falling time is not related to their mass.

　　On your tour you should not miss various places of interest near the Leaning Tower of Pisa including Lucca, Florence, and Santa Maria della Spina.

21．Why does the tower tend to lean to one side?

A．Because the base of the tower was not strong.

B．Because it was originally designed like that.

C．Because many people came to knock it down.

D．Because the builders used lots of soft soils.

22．When is the best time to visit the tower without being disturbed?

A．In summer. B．At night. C．In winter. D．In the morning.

23．What has made the tower much more famous?

A．It will fall to the ground in the near future.

B．It is an obvious engineering failure.

C．Galileo once did experiments on the tower.

D．The restoration lasted more than ten years.

　　B

　　Horses are certainly a marvel (奇异的事物) of creation. They are extremely strong and interact with their environment through their senses. Compared to us, they see better, hear better, have a better sense of smell, and can feel the smallest insect on their bodies.

　　Hearing

　　Horses have excellent hearing, better than that of humans. They can focus one ear on the rider and one ear on something else. Noise created by traffic, wind, and other distractions (分心的事物) can greatly affect their hearing, and cause horses to become skittish. Though horses in more complex environments can be used to disturbing noises after repeated exposure to (暴露于) them, all these sounds and many others can scare horses unfamiliar with them, making it difficult for riders to keep control.

　　Smell

Horses have an excellent sense of smell, much better than that of humans. They may use smell to find their way back. and they can tell differences in the smell of water. Most horses are happy to drink muddy water from a puddle (水坑) because it has a natural smell, but they may refuse to drink from an unfamiliar source. Many riders travel with an old water bucket so their horses will welcome water in the campground.