哪种病原体所致的肺炎在整个病理过程中没有肺泡壁和其它结构的损伤

A、肺炎克雷白杆菌

B、金黄色葡萄球菌

C、放线菌

D、肺炎球菌

E、厌氧菌

A stock priced at $ 20 has an 80 percent probability of moving up and a 20 percent probability of moving down. If it moves up, it increases by a factor of 1.05. If it moves down, it decreases by a factor of 1/1.05. What is the expected stock price after two successive periods（）

A. $ 20.05.

B. $ 22.05.

C. $ 21.24.