The poor boy seems _____ the news that his father died in the car accident for there is no sign of sorrow on his face.

A．not to be known

B．not to have received

C．to have not received

D．not to know

硫化氢试验用于肠杆菌科细菌的鉴别，不产生硫化氢的细菌是（）

A.志贺菌属

B.沙门菌属

C.变形杆菌属

D.枸橼酸杆菌属

E.亚利桑那菌属