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【多选题】
关于点的投影,下列说法正确的是( )A.
点的三面投影不符合三面投影规律
B.
点的投影永远是点
C.
点的正面投影与水平投影的连线一定垂直于 OX轴
D.
点的正面投影与侧面投影的连线一定垂直于OZ轴
E.
点的水平面投影到OX轴的距离等的侧面投影到OZ轴的距离
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【单选题】It is very kind of you to me at the airport.
A.
see off
B.
meet with
C.
see through
D.
see to
【简答题】At first sight the planet Mars(火星)does not appear very welcoming to any kind of life. It has very little oxygen and water, the temperature at night is below 50 degrees and winds of 100 miles(161 kilom...
【单选题】At the first sight the planet Mars(火星)does not appear very welcome to any kind of life. It has very little oxygen and water, the temperature at night is below -50°C and winds of 100 miles per hour cau...
A.
there is no life there now
B.
there is a large amount of water at the poles
C.
the Mars may be able to support life in the future
D.
conditions may have been similar to those on the Earth
【单选题】以下哪个选项描述了克莱门森(Clemmensen)反应?( )
A.
无α-H的芳香醛与具有α—H的脂肪族醛酮进行交叉缩合反应脱水形成α，β-不饱和醛、酮的反应
B.
羰基在锌汞齐浓盐酸作用下，被还原为亚甲基的反应
C.
将醛、酮和肼反应生成腙，再与金属钠或钾在封管或高压釜中加热至较高温度后，把羰基还原为亚甲基的反应
D.
无α-H的醛在浓碱条件下，一分子的醛氧化为羧酸盐，另一分子的醛还原为醇的反应
【单选题】At the first sight the planet Mars does not appear very welcome to any kind of life. It has very little oxygen and water; the temperature at night is below -50℃ and winds of 100 miles per hour cause s...
A.
there is no life there now
B.
there is a large amount of water at the poles
C.
the Mars may be able to support life in the future
D.
conditions may have been similar to those on the Earth
【简答题】Yoga(瑜伽) is a kind of sport.It is very 46 around the world now. Every one can do yoga. It’s good 47 men and women. 48 do people like yoga? It’s 49 to say.. The short answer is that yoga helps you to 5...
【简答题】If you often have a cold, headache or backache, there is something wrong with your health. Eating healthy food 43 good for our health. Tofu（豆腐）, milk, vegetables are healthy for us. Tofu is a kind of ...
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