单项选择题：外径为139.7mm的套管清水增压试压标准（），观察时间30min，压力降落不大于0

外径为139.7mm的套管清水增压试压标准（），观察时间30min，压力降落不大于0.2MPa。

A、10MPa

B、15MPa

C、20MPa

D、25MPa

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Tim was ten years old. He was not a very good pupil, and he did not like __1__ to do homework because he enjoyed __2__ other things in his free time. Frequently he did not do his homework and when he did do it he always __3__ a lot of mistakes. One day his mathematics teacher __4__ Tim's homework and saw that he__5__ all his sums right. He was very pleased and rather __6__ . He called Time to his desk and said to him. "You got all your home work right this time, Tim. What __7__ ? Did you father help__8__ ?" Usually Tim's father did help him __9__ his homework, but the evening before this, he had not been able to, because he had not been at home, so Tim answered, "No,sir, he was very busy last night, so I had to do it all __10__ ."
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