题目

 组成星球的物质是靠引力吸引在一起的，这样的星球有一个最大的自转速率．如果超过了该速率，星球的万有引力将不足以维持其赤道附近的物体做圆周运动。由此能得到半径为R、密度为ρ、质量为M且均匀分布的星球的最小自转周期T。下列表达式中正确的（  ）A．T＝2π        B．T＝2πC．T＝      D．T＝ Bamboo is one of nature’s most surprising plants．Many people call this plant a tree，but it is a kind of grass．Like other kinds of grass，a bamboo plant may be cut very low to the ground，but it will grow back very quickly．A Japanese scientist reported one bamboo plant which grew 1.5 meters in 24 hours ! Bamboo grows almost everywhere in the world except Europe．There are more than 1，000 kinds of bamboo．Not all bamboo looks the same．Some bamboo plants are very thin．They may only grow to be a few centimeters wide while others may grow to more than 3 0 centimeters across．This plant also comes in different colors，from yellow to black to green．Bamboo has been used to make things such as hats and kitchen tools．Because it is strong， bamboo is also used to build buildings．Many Asian countries have used bamboo for hundreds of years．They often use bamboo for buildings and supporting new buildings and bridges while they are being built．In Africa ,poor farmers are taught how to find water using bamboo．These African countries need cheap way to find water because they have no money ,and their fields often die from no rain and no water．Bamboo pipes(管子)help poor farmers bring water to their fields without spending a lot of money．1.How is bamboo like grass?A．It grows quickly． B．It’s wood．C．It is easy to cut． D．It is very thin．2.Though（尽管） you can see bamboo everywhere，it doesn’t grow ．A．in China B．in EuropeC．on mountains D．in Africa3.Bamboo pipes can be used to ．A．make money B．be treesC．grow quickly D．carry water