放大镜的设计原理是采用了：（）
A、凸透镜
B、凹透镜
参考答案：A
如图，在△ABC中，A= 90°，BD是ABC的平分线，DE是BC的垂直平分线，若AD =2 cm，则CD=__________。
The nurse is administering warfarin (Coumadin) to a client with deep vein thrombophlebitis. Which laboratory value indicates warfarin is at therapeutic levels ？（）
A．Partial thromboplastin time (PTT) to 2 times the control.
B．Prothrombin time (PT) to 2 times the control.
C．International normalized ratio (INR) of 3 to 4.
D．Hematocrit of 32%.
A= 90°，BD是
ABC的平分线，DE是BC的垂直平分线，若AD =2 cm，则CD=__________。
to 2 times the control.