到（）时期，火药被开始引入军事战争。
A.春秋战国
B.汉初
C.唐末
D.元代
参考答案：C
Dad _____ lunch at home. [ ]
A. isn't has
B. doesn't has
C. don't have
D. doesn't have
数字仪表的（）属于仪表自身的误差。
A.零点的移动
B.量化误差
C.环境误差
