When is the eof flag raised $($set$/$on$)$ in an input stream object? $($We only know one condition that causes this...$)$

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a

a stream arrives at the end$-$of$-$file marker after a read operation

b

a stream tries to read the end$-$of$-$file marker during a read operation

c

a stream reads past the end$-$of$-$file marker and keeps going