So difficult       it to work out the problem that I decided to ask Tom for    advice.    [      ]

A. I did find      

B. did I find    

C. I have found    

D. have I found

由于心排血量突然下降出现的晕厥为

A．低血糖综合征

B．脑卒中

C．心脏骤停

D．急性心肌梗死

E．阿-斯综合征