称取某石灰石样品20g在高温条件下充分煅烧（杂质不反应），称得剩余固体为13.4g，求该石灰石样品中CaCO₃的质量分数．（提示：石灰石的主要成分为碳酸钙，碳酸钙高温分解的化学方程式为CaCO₃ CaO+CO₂↑ ）

1878年，法国大作家雨果在纪念伏尔泰逝世一百周年的演讲中说：“伏尔泰战胜了敌人。他孤军奋战，打了响当当的一仗，这是一次伟大的战争。”材料中的“伟大的战争”是指（    ）

有些成语，在意思上相对或相似，在结构上却互相对偶，成为十分有趣的四字对，根据示例，给下面的成语分别对上另一个成语。

示例：愚公移山——(精卫填海)

①       无孔不入——____                ②目无全牛——____

②       点石成金——____                ④绳锯木断——____

根据文意及首字母提示补全短文。

    A man walked i____ a doctor's examining room. "Put out your tongue," the doctor said.   

  “OK. There is nothing s____,” the doctor said. "It's clear what's wrong with you.  You need more exercise." “But. doctor." the man said. “I don't think…”

    “Don't tell me what you think," the doctor said “I am the doctor, not you; I know what you need. I see hundreds of people like you. N____ of them get any exercise. They sit in the office all day and in f____ of the television in the evening. What you need is to walk quickly at l____ twenty minutes a day.”

    “Doctor, you don't understand;" the man said “I.”

    “There is no e ____,” the doctor said.  "You must spare some time for exercise. If you don’t, you will get fat and have health problems when you are old.”

    “But I walk every day," the man said.

    “Oh, yes, and I know what kind of walking that is. You walk a few metres to the office from your house, and a few more metres to a r____ for lunch and back.”

    “Please listen to me, doctor!" the man s____ at the doctor angrily.

    “I'm a mailman.”the man w____ on, “I walk for seven hours every day.”

     For a moment the doctor was silent, then he said quietly, "Put your tongue out a____, will you?"