题干

如图表示一神经细胞动作电位和静息电位相互转变过程中的离子运输途径.该细胞受到刺激时,通过④途径运输离子,形成动作电位.下列叙述正确的是(  )

A:由图可知,②③途径属于主动转运

B:④途径的发生只能由电信号引起

C:正常情况下,离子的细胞外浓度高于细胞内

D:静息时,由于①途径的作用,膜电位分布为内正外负

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答案(点此获取答案解析)

A

同类题3

阅读下面短文,从短文后各题所给的四个选项(A、B、C、D)中,选出可以填入空白处的最佳选项。

    People from every corner flooded into the streets that Christmas Eve. “Frosty the Snowman,” and “Jingle Bells” 1 in stores; on the pavements, the street singers performed happily. Everyone, was2 by someone else, delighted and cheerful. I was alone.

    As one of 8 kids of a Brazilian family, brought up in America's crowded apartment, I'd spent several years searching for aloneness. Now, 3, at 27, a college student after the 4 with my girlfriend , every cell inside me wanted to be alone, 5 not at Christmas. My family had 6 to Brazil and my friends were 7 with their own lives. Dusk was approaching, and the fact that I had to return to my 8 home made me sad. Lights from windows blinked, and I hoped someone would 9 from one of those homes to invite me inside with a Christmas tree decorated with shiny fake snow and 10 presents.

    At a market, I felt more 11 when people were buying lots of goods, which 12 the gifts we received as children in my mind . I missed my family and wanted to cry for wanting to be alone and for having achieved it.

    Outside the church , a manger(小耶稣) had been set 13. I stood with others watching the scene, some of them 14themselves, praying. As I walked home, I realized that leaving Brazil was still a painful experience as I struggled with 15 I had become in 15 years in America. I'd mourned the 16, but for the first time, I recognized what I'd gained. I was independent, 17 and healthy. My life was still ahead, full of 18.

    Sometimes the best gift is the one that you give yourself. That Christmas, I gave myself 19 for what I'd obtained up to now and promise to go forward. It is the best gift I've ever got, the one that I most 20.