下列事件是必然事件的是[ ]
A．今年8月8日北京的天气一定是晴天
B．掷一枚硬币，恰好正面朝上
C．到明年，你将增加一岁
D．打开电视，正在播广告
答案：C
— What a pity! You ________ it down on your notebook.
— Oh, my god! I forgot his mobile phone number.[ ]
A. could have written
B. should have written
C. must have written
D. would have written
