消防员在使用消防避火服进行消防作业时,在()情况下,必须用水枪、水炮保护。
A.高温
B.浓烟
C.较长时间
D.有毒
参考答案:C
A fourth market transaction occurs when:()
A. a security is purchased by a dealer and then immediately resold.
B. exchange-listed shares are traded in the OTC market.
C. a buyer and seller complete a trade without the assistance of an intermediary broker.
何谓“卫气同病”?举例说明之。