题目

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 Ways to fight the flu    The flu is annoying enough on its own. In order to keep yourself from it, follow these tips.    ★Get the flu vaccine(疫苗). It’s the best way to protect yourself against the flu.   71  It also helps the people around you because there’s less chance you will catch the flu and pass it on.    ★Wash your hands often. Hand washing is an important way to protect against germs(细菌) like flu viruses.   72 So get in the h为了了解某校初三年级1000名学生的视力情况，随机抽查了部分初三学生的视力情况，经过统计绘制了频率分布表和频率分布直方图．根据图表中的信息回答下列问题：频率分布表分组频数频率3.95～4.2560.124.25～4.55ab4.55～4.85170.344.85～5.15150.35.15～5.4540.08合计501（1）写出频率分布表中的a=______，b=______，补全频率分布直方图；（2）判断这组数据的中位数落在哪个小组内；（3）若视力在4.85～5.15范围内均属于正常，不需要矫正．试估计该校初三学生视力正常的人数约为多少人？