A beekeeper has a        to motivate the bees by leaving some honey in the hive—not so much in case that the bees stop working.

A．trick

B．tool

C．talent

D．desire

观片灯的亮度、颜色及照射野能够改变

A．X线对比度
B．胶片对比度
C．照片对比度
D．生理对比度
E．以上都不是