At first I guessed it was an airplane, but I soon changed my mind because it remained static instead of moving like a plane.()

A. stationary

B. statutory

C. stationery

D. statuesque

铅对⁶⁰钴的γ射线的半价层是1.25cm，若挡铅的厚度是5cm，则挡铅后面的剂量是挡铅前的（）。

A.6.25%

B.12.5%

C.25%

D.50%

E.80%