In zones where earthquakes are known to occur, ______ construction techniques can significantly reduce the effects of seismic wave.

A．to improve

B．improving

C．improved

D．being improving

按照牵引连挂装置的连接方法，车钩可分为（）。

A、自动车钩和非自动车钩； 

B、刚性车钩和半刚性车钩； 

C、过渡车钩和非过渡车钩； 

D、密集式车钩和非密集式车钩。