【单选题】Recently he______ every night until after one o' clock, preparing for the final exam.
【判断题】Gear pumps are fixed displacement pumps.
【判断题】Crescent gear pumps are variable displacement pumps.
【单选题】Gear pumps are of positive displacement type pumps because they discharge a near constant amount of liquid _____ pressure.
【单选题】The hot oils used for frying ______.
A.
is kept fresh every day
B.
may be used for a week
C.
should be changed every 3 days
D.
is changed from hour to hour
【判断题】Some gear pumps are variable displacement pumps.
【单选题】2008年,奥帆赛的火炬共燃烧了( )天,是从( )