[单项选择]施工中应尽量减少立体（）。必需交叉时，施工负责人应事先组织交叉作业各方，商定各方的施工范围及安全注意事项；各工序应密切配合，施工场地尽量错开，以减少干扰；无法错开的垂直交叉作业，层间必须搭设严密、牢固的防护隔离设施。
A. 电焊作业
B. 砼作业
C. 交叉作业
D. 高空作业

Inertial guidance is the name given to those types of systems which guide and keep track of the location of vehicles which are free to move in three dimensions. Vehicles which move only on a plane surface, such as ships or automobiles, require only an accurate compass, sextant, and clock to keep track of their present position. When a vehicle can travel up or down as well as north or east, it is much more difficult to fix its position. An inertial platform is used in inertial guidance to measure vehicle altitude and acceleration which are then integrated to provide position and velocity. The inertial platform consists of three gyroscopes and three accelerometers mounted in the inner gimbal of the four gimbal platform. The purpose of the inertial platform is to allow the vehicle to move in any direction about the inner gimbal containing the gyros and accelerometers, without disturbing or turning them from their original orientation. Thus the gyros and accelerometers do not mm when
A. space in three dimensions.
B. poor visibility and meteorological conditions.
C. the altitude and position of a vehicle.
D. spacecraft productivity.