原子核外电子总数,等于原子核内的( )
A.中子数
B.质子数与中子数之和
C.质子数与中子数之差
D.质子数
在原子中,原子核内的质子数等于原子核外的电子数,观察选项,故选D.
螺旋线得切线与圆柱体轴线得夹角称为(),它是铣削时计算交换齿轮得参数之一。
A.螺旋角
B.导程角
C.螺旋升角
D.螺距
All known techniques for handling complex problems successfully seem to fall into one of the three classes: subdividing the problem (51) , ignoring irrelevant detail in a safe way (52) , and having an independent agent (53) the internal consistency (contextual checking). The first two provide guidelines for solving the problem, the third serves to provide early warnings. A good programming language supports all three. In subdividing problem, some of the subproblems may be similar to the (54) problem. It leads us to a (55) solution. This (55) solution is viable provided each of the subproblems is easier to solve than the original problem.
A. abrogation B. abstraction C. composition D. contraction