电化学加工应用于模具制造，按其作用原理可分为（）、（）、化学腐蚀加工法。
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三极管基极的作用是（）载流子。
A. 发射
B. 输送和控制
C. 收集
D. 产生
A block and tackle is rove to advantage. This means that the（）.
A. blocks have been overhauled
B. hauling parts of two tackles are attached
C. hauling part leads through the movable block
D. hauling part leads through the standing block
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