Complete with FOR or SINCE: Have you been studying Japanese _____ many years?
for
Complete with FOR or SINCE: They've been running ____ hours!
for
Complete with FOR or SINCE: He's been making videos _____ he was 4.
since
Complete with FOR or SINCE: He's been collection autographs _____ he moved to LA.
since
That dog smells awful- what has it been doing? _____ ______ ______ (roll) in the mud.
IT'S/IT HAS BEEN ROLLING in the mud.