如图所示，用动滑轮把一个物体匀速拉起，不计摩擦，则下列说法中正确的是（ ）
A．使用这个滑轮可以省功
B．使用这个滑轮可以省距离
C．拉起的物体质量越大，滑轮的机械效率越高
D．把物体拉起的越高，滑轮的机械效率越高
答案：C
题目分析：A、使用任何机械都不能省功， A错误，不符合题意；B、动滑轮是省力杠杆，可以省力，但费距离． B错误，不符合题意；C、在动滑轮一定时，提起物体的重力越大，机械效率越高．物体质量越大，物重越大，机械效率越高，符合题意；D在物重一定时，动滑轮重越小，所做额外功越小，机械效率越高，与其它因素无关， D错误，不符合题意，答案选C．
阅读下面短文，从方框内选择恰当的句子填入短文空白处，使短文内容完整、意思连贯。 Where do our favorite foods come from? The truth may surprise you. Did you know curry isn’t Indian? Did you know Americans weren’t the first to eat hamburgers? Or did you know pizza wasn’t created in Italy? First, let’s talk about curry. 小题1: But in reality(事实)， wealthy English people were cooking with curry spices (香料) hundreds of years before British ships traveled to India. 小题2: Cooks of wealthy English families created curry dishes, and later these dishes became popular in other parts of England. 小题3: The Persians were eating round, flat bread with cheese in the 500s-nearly  one thousand years before pizza became popular in Naples, Italy!Finally let’s look at the truth behind hamburgers. Many people think hamburgers are an American food. 小题4: A German named Otto Kuasw made the first hamburger in 1891. Four years later, German sailors introduced hamburgers to Americans. Where foods come from isn’t nearly as important as how they taste—delicious! 小题5:
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