He opened his mouth as if ____.[ ]
A. to speak
B. to speaking
C. said
D. was speaking
答案:A
一般,状态估计的步骤包括()。
A.建立数学模型
B.状态向量的估计计算
C.不良数据和结构误差的检测
D.不良数据和结构误差的识别
油、气、水井可分为哪五类?