题干

分类法在化学的发展中起到非常重要的作用,下列分类标准合理的是
①根据氧化物的组成元素将氧化物分成酸性氧化物、碱性氧化物和两性氧化物
②根据反应中是否有电子转移将化学反应分为氧化还原反应和非氧化还原反应
③根据分散系是否有丁达尔效应将分散系分为溶液胶体和浊液
④根据反应中的热效应将化学反应分为放热和吸热反应
⑤根据水溶液能否导电将化合物分为电解质和非电解质   

A:②④

B:②③④

C:①③⑤

D:①②④⑤

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A

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    In high school, all Canadian students take part in a very exciting event. It is "Take Your Children to Work Day". Students will have a chance to work with their parents. My day took place in my mom's work, the York Region Police Department.

    When I arrived, a coach was teaching the officers basic combat(格斗)skills. Everyone tried their best to practice. I could see them sweating and panting (喘气).

    The most exciting part of my visit was a stop at the 911 Communication Center. 911 is the same as 110,119 and 120 in China. Every 911 call in the city is answered here. When I entered the center, I stood beside a call dispatcher (分派人员)arid watched him dealing-with the calls.

    Suddenly, the phone rang, he picked it up and a woman cried for help. There was a robbery in her house. The call dispatcher told her, "Please calm down and move to the safe place quietly. Don't fight with them. Just let them take what they want. Please make sure you are not hurt. We are sending officers there."

    He followed the call and found the address. The call dispatcher chose the five closest police cars from the satellite map and clicked(敲键盘) to send the policemen.  I saw the police cars from the satellite map were quickly moving to the woman's house. Five minutes later, they arrived .I asked the call dispatcher why he sent five cars. He said, "There are different levels of emergencies. Robbery is a high priority (优先),so we have to send five cars." The day was interesting. I leaned how the different departments worked together. The officers were very friendly and admirable.