Those black clouds are a sure _____ that it’s going to rain. 
#6678
A
thing
B
mark
C
sign
D
one
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 We have spent _____ money on English books.
#6895
A
a great deal of
B
a good many
C
a plenty of  
D
a number of
Please refer to the   before you switch on the engine.
#5486
A
introductions
B
explanations
C
instructions
D
expressions