How many ______________ are there in the picture?[ ]
A. a bus
B. buses
C. bus
D. some bus
答案:B
由5个千、8个0.1和3个0.001组成的数是______.
THDS-A探测系统中光子探头工作方式为()
A、直流探头
B、调制探头
C、热敏探头
D、热释电探头