‍According to source, composite materials divided into: （）‎ A: conductive composite materials B: natural composite materials C: artificial composite materials D: damping composites

When the system vibrates in a fluid medium, the damping is ( )a)Viscous b) Columb c)Solid d)Fluid A: None B: None C: None D: None

For a MDOF system, which one is needed to calculate its vibration frequencies? A: the mass matrix [M] B: the damping matrix [C] C: the stiffness matrix [K] D: the vibration modes

副翼作动器内部的电磁活门作动后，作动器处于（）。 A: 工作模式ACTIVE B: 备用模式STANDBY C: 阻尼模式DAMPING D: 定中模式CENTERING

副翼作动器内部的电磁活门作动后，作动器处于（）。 A: A工作模式ACTIVE B: B备用模式STANDBY C: C阻尼模式DAMPING D: D定中模式CENTERING

In general, the damping ratio of steel structures is than that of the reinforced concrete structure. That is, the seismic action of the steel structure is than that of the reinforced concrete structure under the same structure period, mass and other parameters. ( ) A: smaller smaller B: smaller larger C: larger smaller D: larger larger