题干

为除去括号内的杂质,下列所选用试剂和方法均正确的是(   )

A:Na2CO3溶液(NaHCO3),加热

B:铁粉(铝粉):加入过量的氨水后过滤

C:NaCl溶液(Na2SO4):加入适量的硝酸钡后过滤

D:淀粉溶液(KCl):通过半透膜进行渗析

上一题 下一题 0.0难度 选择题 更新时间:2019-12-29 09:01:22

答案(点此获取答案解析)

D

同类题1

完形填空

    Yesterday was Father's Day. Many things happening between my father and me crowded my mind. But one thing made a deep impression on me.

    It was a Sunday morning, and I was in a 1 mood (情绪). Two of my friends had gone to the movies the night before and hadn't invited me.I was in my room2ways to make them sorry when my father came in. “ Want to go for a ride today,Berk? It's a beautiful day.”

    “No! Leave me alone!”Those were the 3words I said to him that morning.

    My friends called and 4 me to go to the mall with them a few hours later. I forgot to be5with them and then went with them.When I came home,I found a6 on the table.My mother put it where I would be sure to see it. “ Dad has had an 7 Please meet us at Highland Park Hospital.”

    When I reached the hospital ,my mother came out and told me a car hit my father and his injuries were extensive(大曲积的). “Your father told the driver to leave8 alone and just call 911, thank God! If he had moved Daddy, ….”

    My mother may have said more,but I didn't hear. I didn't hear anything 9 those terrible words: Leave me alone. My dad said them in order to10 himself. He didn't want to be hurt more. How much had I hurt him 11 I shouted out those words at him earlier in the day?

    It was several days later that he was12 able to have a talk.I held his hand gently, afraid of hurting him.

    “ Daddy... I am so sorry...''

    “It's okay, sweetheart. I'll be okay.”

     “No,” I said, “I mean about13 I said to you that day.You know, that morning?"

    He looked at me and said, “Sweetheart, I remember14 about that day, not before, during or after the accident. I remember telling you goodnight the night before,though." He managed a weak smile.

    My English teacher once told me that words have great power. They can hurt or they can heal(治愈).And we all have the power to 15 our words.I am going to do that very carefully from now on.

同类题4

任务型阅读

    With busy lives, it can be hard to find time to volunteer. However, the benefits of volunteering are great to you, your family, and your community(社区).

    One of the better-known benefits of volunteering is the effect on the community. Volunteering allows you to connect with your community and make it a better place. Volunteering also strengthens your ties to the community and broadens your support network, exposing(使暴露) you to people with common interests, neighborhood resources, and fun and satisfactory activities.

    While some people are naturally outgoing, others are shy and have a hard time meeting new people. Volunteering gives you the opportunity to practice and develop your social skills, since you are meeting regularly with a group of people with common interests. Once you have the desire, it's easier to make more friends and contacts.

    Volunteering provides many benefits for both mental and physical health. You're doing good to others and the community, which makes you experience the pleasure of success. Your role as a volunteer can also give you a sense of pride and identity.

    Reducing the risk of depression(沮丧) is another important benefit of volunteering. A key risk factor for depression is social isolation. Volunteering keeps you in regular contact with others and helps you develop a solid support system, which in turn protects you against stress and depression when you're going through challenging times. Volunteering is good for your health whether you are young or old, but it's especially good in older adults.

    Volunteering offers you the chance to try out a new career without making a long-term commitment. It is also a great way to gain experience in a new field. Volunteering work can expose you to professional organizations or internship(实习)that could be of benefit to your career. That volunteer work is unpaid doesn't mean the skills you learn are basic. Many volunteering opportunities provide training. In addition, volunteering can also help you build upon skills you already have and use them to benefit the greater community.

    Volunteering is a fun and easy way to explore your interests and passions. Volunteer opportunities that match both your goals and your interest are most likely to be fun and satisfying for you. Doing volunteer work you find meaningful and interesting can be a relaxing escape from your day-to-day routines of work, school, and family commitments. Volunteering also provides you with renewed creativity, motivation, and vision that can be carried over into your personal and professional life.