设有9个硬币，其中有1分、5分、1角以及5角四种，且每种硬币至少有1个。若这9个硬币总值是1．77元，则5分硬币必须有几个( )
A．1
B．2
C．3
D．4
参考答案：C
解析：每种硬币至少有1个，则知四种硬币各1个共0.66元，总值为1.77元，则需增加1.11元，从而需硬币1分1个，硬币5角2个，最后还需1角，从1角硬币1个或2个5分硬币中选择，题意要9个硬币，宜选择2个5分硬币，因而有3个5分硬币。故答案为C。
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| Returning from a trip overseas, I sensed that something was wrong between Keith and me. So I asked him, "Keith, have I done anything that really 1 your feeling?" Immediately, he said, "Yes. Last Christmas you promised us a special 2 that I really wanted but you 3 gave it to me." The 4 was that I'd completely forgotten about it. I 5 , "Is there anything else I've done wrong, but didn't apologize for?" Again, his 6 was immediate, "Remember last Christmas when Mom said you had to go to the 7 because Stephen was going to be born? You left us at home and 8 in a hurry. Remember?" "Well, you left and 9 the suitcase." I couldn't believe he 10 all the details! "After you came back from the hospital you were 11 . When you got home, the suitcase had been opened and 12 had been thrown all over the place. And you 13 me." "And you didn't do it?" I asked. "No, I didn't. I was just searching for my gift." My heart sank. I felt 14 . I hugged Keith and asked him to 15 me. His honesty made me think of our other son, Kevin. Maybe I'd hurt his feelings, too. I went to ask him the 16 question. Kevin's answer was as immediate as his 17 , "Last Christmas you 18 us a special toy, but you forgot about it." 19 Christmas had passed, I took my two sons to the store that day and bought them what I had promised. The 20 thing wasn't the toy. The problem was I'd made a promise too lightly and didn't keep it as their father. | ||||
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