四行程发动机完成进、压、爆、排四个动作，产生一次动力，其活塞在汽缸中上下运动各（）。
A.一次
B.两次
C.三次
D.四次
参考答案：B
患者杨某，痢下赤白粘冻，白多赤少，腹痛，里急后重，饮食乏味，饱闷，头身重困，舌质淡，苔白腻，脉满缓。证属
A．寒湿痢
B．休息痢
C．噤口痢
D．虚寒痢
E．阴虚痢
An investor purchases a stock for $40 a share and simultaneously sells a call option on the stock with an exercise price of $42 for a premium of $3/share. Ignoring dividends and transactions cost, what is the maximum profit that the writer of this covered call can earn if the position is held to expiration
A．
B．
C．
