They often play ping-pong on weekends.（对play ping-pong提问） 为什么要写they often do on weekendsThey often play ping-pong on weekends.（对play ping-pong提问） 为什么要写what do they often do on weekends
问题描述：
They often play ping-pong on weekends.（对play ping-pong提问） 为什么要写they often do on weekends
They often play ping-pong on weekends.（对play ping-pong提问） 为什么要写what do they often do on weekends
答
因为提问是对play ping-pong提问的，所以DO用来提问PLAY，而PLAY是主语
答
What do they often do on weekends ?
答
what do they often do weekends