题干

生长旺盛的叶片,剪成5毫米见方的小块,抽去叶内气体,做如下图所示处理,这四个处理中,沉入底部的叶片小块最先浮起的是(    )

A:

B:

C:

D:

上一题 下一题 0.0难度 选择题 更新时间:2019-05-13 01:09:38

答案(点此获取答案解析)

C

同类题3

阅读理解

    “My dear lady,”says Holmes.“You're shivering.Are you cold? Do you want a cup of hot tea?”

    “I'm not cold,”the woman replies,“I fear for my life!”

    “We are here to help you.Don't worry about anything.I don't know you.But I know many things about you.For example,I know how you traveled.You came to London by train.You also rode to the train station on a horse—drawn wagon.''

    “Why,yes.You‘re right.But how do you know these things?”

    “I see a return ticket in your glove.I see fresh mud on the left arm of your dress. Now tell us your problem.''

    “My name is Helen Stoner,”she states,“My mother and father are dead.I am living with my stepfather.Dr.Grimsby Roylott.He comes from a rich family.But they are no longer rich.They have nothing except a small piece of land and a huge old house.We are living in the house. Dr.Roylott is using my mother's mone37 for expenses.Part of it was for my sister and me. It was for our marriages.”

    Holmes is sitting in his chair.His eyes are closed.He is listening carefully to Helen's story.He hears every detail.

    Helen continues. “My stepfather has no friends.He fights with everyone.He is strong and gets angry quickly. Everyone is afraid of him.”

    “He has no friends at all?”asks Holmes.

    “No.He talks to no one except the gypsies(吉普赛人).They are poor people who travel from place to place.A band of gypsies is staying on our land right now.''

    “Are you and your sister afraid of the gypsies?”

    “My dear Mr.Holmes.You are making me so sad.My sister is dead.That is why I am standing here in this room.”    ,  .