The flood is a bit____the safety level. a.below

The flood is a bit____the safety level. a.below

below （数量、比率或水平）低于，小于，少于 If something is below a particular amount, rate, or level, it is less than that amount, rate, or level.
Night temperatures can drop below 15 degrees Celsius... 夜间气温会降到15摄氏度以下。
British Telecom agreed to keep overall price increases to 7.5 per cent below inflation... 英国电信同意将整体价格增幅控制在低于通货膨胀7.5%的水平。
Rainfall has been below average. 降雨量低于平均水平。
（数量或度量）在…以上，超过【用above】追问回答非常认真和专业！ 不会是老师吧？非常感谢！追答高中英语老师

在这里超出不能用over，而应该用beyond，你可以理解成习惯用法

其实不必计较太多，只要明白考试是选最佳答案，而不是正确答案。
这道题其实a,b,d都没错，在日常生活中这三种说法都有。
比如：age below sixteen, age under sixteen, too much over the normal standard, over the normal level, exceed the normal level, score 90 marks or below,