呕血(haematemesis)
参考答案：
上消化道出血时，胃内或返流入胃内的血液经口腔呕出称为呕血。
Circus tigers, although they have been tamed, can _____ attack their trainer.
A．unexpectedly
B．deliberately
C．reluctantly
D．subsequently
普通水平仪的水准器上刻度值为（）。
A.0.02mm／m
B.0.04mm／m
C.0.05mm／m
D.0.06mm／m
