单项选择题
A.heavy
B.easily damaged
C.affected by temperature
D.costly relative to the strength ratio
单项选择题 A device fitted over the discharge opening on a relief valve consisting of one or two woven wire fabrics is called a flame（）.
单项选择题 A decrease in barometric pressure is associated with all of the following except（）.
单项选择题 （）during the voyage any case or suspected case of plague，cholera，yellow fever，smallpox，typhus or relapsing fever?