如果正常运行时向系统输出无功为Q1,失步运行后由系统吸收无功为Q2,则系统出现(Q1+ Q2)的无功缺额。( )
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It was not until 3:00 pm______ the secretary found the missing report.
A) where
B) as
C) that
D) while
The police have not ______the search even if it has lasted for a week.
A) given up
B) broken in
C) taken away
D) brought about
I decided to _____as a waiter in a restaurant during my summer vacation.
A) serve
B) take
C) turn
D) make
I’m afraid we don’t have that book in stock, ______we can order it for you.
A) as
B) since
C) but
D) for