Sixteen-year-olds should not be allowed to drive because they aren't＿＿at that age.

B
首先不允许,是因为能力不够.所以C和D用much显然不合适
enough + 形容词 ,enough要放在形容词之后.所以,A不对
16岁不允许开车因为在那个年龄人们还不够严肃认真（16岁不知道后果.不知道负责人）帮我补个enough 的所有用法，谢谢~1. 用作名词，表示“足够(的数目或数量)，没有复数形式，但根据情况可表示复数意义。如：Enough has been said about this subject. 关于这个问题已说得够多了。Enough were present to constitute a quorum. 出席的人数够法定人数。2. 用作形容词，通常修饰复数名词或不可数名词，可放在被修饰名词之前或之后(但以前置为多见)。如：He has enough money to buy a car. 他有足够的钱买辆汽车。We have time enough to get to the airport. 我们来得及赶到机场。【注】有时与某些具有形容词意味的名词连用，此时 enough 必须后置，且该名词通常不用冠词。如：I was fool [=foolish] enough to accept his offer. 我接受他的提议真是太傻了。3. 用作副词，可用来修饰形容词、副词、动词等，此时总是放在被修饰语之后。如：He didn’t practise enough. 他练习得不够(from www.et777.cn)。She isn’t good enough for [=to pass] the exam. 她的功课还不够好，还考不及格。I don’t know him well enough to ask him for help. 我和他不够熟，不能请他帮忙。其后可接不定式或介词 for, 但一般不接that-从句。如：在这条河里游泳水够深吗?正：Is the river deep enough to swim in?正：Is the river deep enough for swimming in?误：Is the river deep enough that people can swim in?在口语中，出于客气和礼貌，人们常用类似于下面这样的句型:Would you be kind enough to open the window? (=Would yoube so kind as to open the window?) 请你打开窗户好吗?4. 在通常情况下，enough 不能用作表语，除非其主语是代词或是那些具有(或暗示有)数量意义的名词。如：That’s enough. 够了(from www.et777.cn)。One such dictionary is enough. 这样的词典一本就够了。Six bottles of wine will be enough. 六瓶葡萄酒就够了。比较下面的正误句子：误：The beer isn’t enough. 啤酒不够。正：There isn’t enough beer. 啤酒不够。误：Was the time enough? 时间够吗?正：Did you have enough time? 你们时间够吗?