题目内容：
完成题 通读下面的短文，掌握其大意。然后，从每小题的四个选项中选出可填入相应空白处的最佳选择，并把它前面的大写字母填入左边的括号里。
Sometimes I feel that being the mother of three small children is like operating a large cir- cus(马戏团)． 21________ afternoon last week，my three sons were playing peacefully in the back yard(院子)，22________the ball from one to another． I jumped at the chance to talk to one of my friends 23________ the phone，but before I 24________ to the phone，I could tell the boys had begun to quarrel with each other about something．I rushed out to 25 ________peace，but before I got there Charles had 26________ a rock at Mark，and hit him in the eye．By the time I got to the back yard，they had begun to 27 ________about this．Even David，the oldest boy，who won’t usually fight with anybody about 28________，was involved(卷入)．First，I 29________ them stop fighting，and then I examined Mark’s eye．I decided that it wasn’t going to develop into a black eye．But I felt that they should 30 ________ at least a little for 31________ they had done．“I'm going to 32________ to your father about this when he comes home tonight，”I said．“He and l will think of how to punish you．”Things were 33 ________ quiet after that for about half an hour，and then Charles 34 ________ a glass in the kitchen，and at almost the same 35________ ，Mark fell out of the apple tree．
21． A．Certain
B．A
C．some
D．One
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答案解析：