问题
不定项选择
如图所示，CD为插入地面的排球网架直杆，为了使杆垂直于地面，还要用绳子把杆拉住。假定绳子OA、OB、OC是在同一平面内，OA与OB两绳的拉力相同，夹角为60°。绳能承受的拉力跟绳的横截面积成正比，那么OC绳的直径至少应是OA绳的几倍才是合理的？（结果保留2位有效数字）
A．2.0
B．3.0
C．1.3
D．2.4
答案
答案：C
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如图所示，CD为插入地面的排球网架直杆，为了使杆垂直于地面，还要用绳子把杆拉住。假定绳子OA、OB、OC是在同一平面内，OA与OB两绳的拉力相同，夹角为60°。绳能承受的拉力跟绳的横截面积成正比，那么OC绳的直径至少应是OA绳的几倍才是合理的？（结果保留2位有效数字）
A．2.0
B．3.0
C．1.3
D．2.4
答案：C
| 根据表格内容完成下列短文。 | ||||||||||||||||
| It's useful to know how much money we usually spend on different things. Then, if we also know how much money we will have, we can decide which things we should buy now and which things we can go without or wait for. Here is a student's weekly budget (预算) during the school year.
have them at all. If he wants to save (节省) on bus fares, he can 1______ to class. If he doesn't buy any candy, he can save 2______ a week. Or he can save 3______ if he has no soft drinks. He can save on lunches if he brings his own. He may be able to save on VDs by borrowing them from his friends or 4______ second-hand (二手). He doesn't have to 5______ to the movies or restaurants. |