单项选择题
A.1个HVL B.2个HVL C.4个HVL D.5个HVL E.6个半HVL
A.80% B.85% C.90% D.95% E.100%
A.±0.1cGy B.±0.5cGy C.±1cGy D.±2cGy E.±5cGy