科学课上，某同学将一包主要原料为柠檬酸（C₆H₈O₇）和小苏打的汽泡真粉 末倒入玻璃杯中，加入200mL冷水，看到有大量气泡快速生成，待粉末完全溶解，就得到一杯果味饮料

（1）柠檬酸 ____种元素组成．

（2）其中碳、氢元素的质量比为 ____．

今年春季以来，我国许多城市雾霾天气频发，PM2.5是造成雾霾天气的“元凶”之一．PM2.5是用来监测空气中下列哪项含量的（　　）

根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    Mr and Mrs Yates had one daughter.   1   name was Carol, and she was nineteen years old. Carol lived  2 her parents and worked in an office. She had some friends, but she  3any of the boys very much.

    Then she met a very  4 young man. His name was George. and he  5  in a bank near her office. They went out together quite  6 , and he came to Carol’s parents’ house twice, and then last week Carol went to her father and said, “I  7 George, Daddy. ”

    “Oh, yes,” said  8  .“he’s a nice boy. But has he got any money?”

    “Oh, men! All of you are  9  ,” the daughter answered    10  . “I met George on the first of June and on the second he said to me, ‘Has your father got any money?’”