There _____________ a pen and two pencils in the box. [ ]
A. are
B. is
C. has
D. have
答案:B
Under perfect competition, a firm will experience zero long term economic profit when:()
A. price is less than average total cost.
B. MR is greater than ATC.
C. MC = ATC = MR = price.
男性,58岁,有高血压病史,于情绪激动后,突然出现头痛、呕吐,左侧肢体活动不利,随之意识不清,血压190/110mmHg,瞳孔不等大,右侧大于左侧,左侧肢体瘫痪,最大可能的诊断是
A.脑栓塞
B.脑出血
C.TIA
D.脑血栓
E.蛛网膜下腔出血