With some technical problems to be solved, it may be a while _______ the system is put into use.
"I usually go there by train." "Why not ______ by boat for a change?"
"What do you think of the book?" "Oh. excellent, it's worth _______ a second time."
People couldn’t help ______ the foolish girl.
Excuse me for _____ in without ______.
Most of the students enjoy_____ stamps.