患者，男，49岁。呕血、黑便2天；晕厥1次，患者面色苍白，四肢湿冷，心率110次/分，血压90/60mmHg，小便少，估计失血量是（）。

A.400mL

B.500mL

C.600mL

D.700mL

E.800mL

For markets with perfectly elastic supply, the introduction of a tax will most likely result in:（）

A. a price increase and the seller pays the entire tax.

B. a price increase and the buyer pays the entire tax.

C. no change in price and the seller pays the entire tax.