题干

科学家探究不同浓度醋酸铅对小鼠胸腺细胞凋亡率的影响,结果如表.

组别

醋酸铅溶度(m/L)

胸腺细胞凋亡率(×10﹣4

0

 0.35±0.05

 125

 1.03±0.52

 250

1.65±0.40

 丁

500

3.08±0.56

下列分析正确的是(  )

A:甲组为实验组,乙、丙、丁三组为对照组

B:醋酸铅的浓度是因变量,胸腺细胞凋亡率是自变量

C:小鼠在正常的生活环境中胸腺细胞不会发生凋亡

D:实验说明醋酸铅可导致小鼠胸腺细胞凋亡率升高,且凋亡率与浓度呈正相关

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答案(点此获取答案解析)

D

同类题1

阅读下面短文,从短文后各题所给的A、B、C、D四个选项中,选出最佳选项。

     Although it was autumn, the snow was already beginning to fall in Tibet (西藏). Our legs were so heavy and cold that 1 felt like big pieces of ice. Have you 2 seen snowmen ride bicycles? That's what we looked like! Along the way children who were 3 long wool coats stopped to look at us. In the late4 we found it was so cold that our water bottles froze (结冰).However, the lakes   5 like glass in the setting sun and looked wonderful.

    Wang Wei rode in front of me as usual. She was in high spirit and I knew I didn't need to

    6 her. To climb the mountains was hard work but as we7 us, we were surprised by the view. We seemed to be able to see for miles, and we were so high that we found ourselves cycling through clouds. After a while, we began going 8 the mountains. It was great fun especially as it slowly became much 9. At the foot of the mountains, colourful butterflies flew around us and we saw many sheep eating green grass. Then we had to 10 our caps, gloves and trousers for T-shirts and shorts.

    In the early evening we stopped to make camps. We 11 our tent(帐篷)and then we ate. After supper Wang Wei went to sleep but I stayed 12.  13 midnight the sky became clearer and the stars grew brighter. As I 14 below the stars I thought about how far we had already travelled.

    We will reach Dali in Yunan Province soon, where our cousins will join us. We 15 hardly wait to see them!