单项选择题
An instrument that maintains a continuous record of humidity changes is called a（）.
A.thermometer B.barometer C.hygrograph D.thermograph
单项选择题 An instrument that indicates wind direction is known as a(n)（）.
单项选择题 All of the following steps are taken in starting a centrifugal pump，EXCEPT to（）.
单项选择题 After an engine is started you should（）.
