We must do something to ________ the factories sending out poisonous gases so as to keep the city clean and beautiful.

A．keep

B．protect

C．permit

D．prevent

出血性与缺血性脑血管疾病的鉴别，除临床表现外，最有诊断意义的辅助检查是

A．血常规

B．头颅CT

C．腰穿

D．经颅多普勒超声

E．脑电图