He devoted himself __________ to his research and got many achievements

________，he never seems able to do the work beautifully

Does John serve in the army?—No, but he________in the army for 8 years

Jenny, I’ve finished my summer school classes—Well, Chinese is _______ difficult to learn, isn’t it?—It seemed that _______ at first But after a while it starts to get easier I got an A in the exam

The small boys decided ______ to each other.