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【单选题】
According to myth, Rwandas ancient line of kings descended from a man with secret knowledge: He could【B1】______ordinary rock into smooth, gleaming iron.【B2】______this new technology, he taught his people to make hard, durable weapons for defeating their enemies and sharp axes for cutting the forest to make fields. By the time the first Europeans arrived in the 19th century, iron had become【B3】______in the kingdom of Rwanda Other traditional African societies tell stories of【B4】______ironworkers who descended from heaven or came from other lands. The prevalence of such legends【B5】______the importance of ironworking in these cultures, and archaeologists have long wondered if the arrival of iron metallurgy【B6】______the growth of complex early societies. Did foreigners【B7】______bring ironworking to Africa, or did Africans invent it themselves? Entering the Iron Age was not easy. Metalworkers had to melt ore at【B8】______temperatures and then repeatedly hammer and reheat the spongy metal. The traditional view is that metallurgists in Turkey were the first to melt iron ore【B9】______, beginning around 1800 B.C.E. Initially, they【B10】______the new metal for precious【B11】______or ritual objects. But by 1200 B.C.E., workers in the Levant were boiling out【B12】______amounts of iron. The metal had a major【B13】______on societies. Iron was a transformative metal. Iron ores are much more【B14】______than copper or the tin needed to make bronze. Bronze was【B15】______costly and largely limited【B16】______use in ritual objects and goods for【B17】______. But once cultures learned to melt iron, they could put iron tools into the hands of【B18】______people for clearing forests and tilling the【B19】______. This boosted agricultural yields, increased the numbers of villages, and【B20】______ever more social complexity. 【B1】
A.
manipulate
B.
magnify
C.
transplant
D.
transform
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【单选题】熔化极二氧化碳气体保护焊,碳钢中厚板横位对接接头、V形坡口、封底层焊接时,选用直径1.2mm的药心焊丝,焊接电流的选择范围一般为( )
A.
80-120 A
B.
120-160A
C.
160-200A
D.
200-240A
【单选题】熔化极二氧化碳气体保护焊,碳钢中厚板横位对接接头、V形坡口、中间及盖面层焊接时,,选用直径1.2mm的实心焊丝,焊接电压的选择范围一般为( )
A.
A17-21V
B.
21-25V
C.
25-30V
D.
14-17V
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A.
高浓度无机盐
B.
低浓度无机盐
C.
高浓度的铵根离子
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A.
职业劳动
B.
体力劳动
C.
脑力劳动
D.
创立事业
【判断题】White培养基的特点是无机盐浓度较高,适于生根培养。
A.
正确
B.
错误
【单选题】熔化极二氧化碳气体保护焊,碳钢中厚板横位对接接头、V形坡口、中间及盖面层焊接时,,选用直径1.2mm的实心焊丝,焊接电流的选择范围一般为( )
A.
80-120 A
B.
120-160 A
C.
160-200A
D.
200-240A
【单选题】21 White培养基的特点是( ) 。
A.
高浓度无机盐
B.
低浓度无机盐
C.
高浓度的铵根离子
D.
低浓度金属离子
【单选题】熔化极二氧化碳气体保护焊,碳钢中厚板横位对接接头、V形坡口、中间及盖面层焊接时,,选用直径1.2mm的药心焊丝,焊接电流的选择范围一般为( )
A.
80-120
B.
120-160A
C.
160-200A
D.
200-240 A
【简答题】竞争者从需求角度可分为愿望竞争者、普通竞争者、产品形式竞争者和 [填空(1)] 。A. 品牌竞争者
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A.
100-140A
B.
140-180A
C.
180-220A
D.
70-100A
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