两颗靠得较近的天体称为双星．宇宙中有某一对双星，质量分别为m₁、m₂，它们以两者连线上某点为圆心，各自做匀速圆周运动，已知两双星间距离为L，不考虑其他星球对它们的影响．则星体m₁的轨道半径r₁=______；和它们运动的周期T=______．

Quality planning tools are often used to help plan effective quality management activities.（）is one of such tools,which involves comparing actual or planned project practices to those of other projects to generate ideas for improvement and to provide a basis by which to measure performance.

A.Benchmarking

B.Quality metric

C.Quality checklist

D.Brainstorming