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问题 选择题

设NA代表阿伏加德罗常数，下列说法正确的是（   ）

A．2.4 g金属镁变成镁离子时失去的电子数目为0.1NA

B．2 g氢气所含原子数目为NA

C．1 mol MgCl2固体溶于水中，所得氯离子的数目为NA

D．17 g氨气所含电子数目为10NA

答案

答案：D

镁在反应中失去2个电子，A不正确。B不正确，2个氢气是1mol，含有2mol氢原子。C不正确，氯离子数目应该是2NA。所以正确的答案选D。

选择题

下列对孟德尔选用豌豆做遗传实验容易取得成功的原因，叙述不正确的是[ ]

A．豌豆具有稳定的．容易区分的相对性状

B．豌豆是自花传粉而且是闭花授粉的植物

C．豌豆在杂交时，母体不需要去雄

D．豌豆一般都是纯种，用豌豆做人工杂交实验，结果既可靠又容易分析
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单项选择题

B


It keeps your insides from falling out. It helps you warm up when you are cold, and it can cool you off when you are hot. It lets you feel things by touch.
What is this Your skin, of course! What does your skin ask for in return for all the wonderful things it does Just a little care! So let’s learn how to take good care of our skin.
Like the heart and stomach, your skin is an organ(器官). In fact, it is the largest organ in your body. Unless there’s a problem, you may not think about your skin very much. But skin has an important job to do.
Your skin is protecting you. Your skin keeps you from getting sick. When you take care of your skin, you are helping your skin do its job. Taking care of your skin today will help you have no problems in the future.
Clean skin is happy skin! One simple way to take care of your skin is to keep it clean. Keeping your hands clean is very important. When washing your hands, use warm water. Wet your hands, and then use soap. You should wash your hands carefully everywhere.
You’ll also want to use warm water, but not too hot, when you take a bath. Use soap to clean your body. Don’t forget under your arms and behind your ears! Your face needs attention, too. It’s a good idea to wash your face once or twice a day with warm water.

What’s one of the simple ways to look after your skin ( )

A．Use warm water.

B．Keep it clean.

C．Wash it twice a day.

D．Use soap.
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