多久一次
how often is───多久一次
it is often───经常是这样
it often───它经常
so it is often───所以经常这样
how it is───怎么回事
how is it───怎么样
how many is it───有多少
how nice it is───多好啊
how fun it is───多有趣啊
Who maintains the aircraft and how often is it serviced? Is the maintenance conducted by factory-authorized service centers or not?───谁来维护飞机且频率如何？维护是否由原厂授权的服务中心执行？缛。
is often difficult to discern how widespread public support is.───了解公众支持的广泛程度常常是困难的。
There is often an inverse relationship between the power of the tool and how easy it is to use.───工具的功能越强大，操作起来往往越费事。
Is there a QA laboratory? What equipment is in the laboratory? How often is it checked and calibrated ?───是否有化验室？化验室具备哪些检测设备？多久对它们进行一次检查和校准？。
because it keeps the body strong. like sports with teams. how often is it good to play a sport?───因为他拥有强壮的身体，喜欢团队运动。多久运动一次才好呢？
how often is it good to play a sport?───做运动要怎么样经常做才好？