—What's the man ___?
—I don't know. [ ]
A. talking
B. waiting
C. taking
D. listening
答案:C
绝对误差它可能是正值,也可以是负值,它的符号决定于测得值的大小。
芯子如果不烘干,可使铸件产生();
A、缩孔;
B、冷隔;
B、气孔;