There is a system ________the waste is disposed of using the principles of ecology.
“Meals on wheels” is a free service, ____ hot meals are delivered to elderly people who may not be able to move around very easily.
To her disappointment, what she had devoted herself to ____ in nothing but failure.
–Did you see ____ English teacher? --I saw him at ____ work in the office just now.
When ____ a new word, you’d better _____ a dictionary.
After the quarrel, I tried all my best to fix the misunderstanding between us, but all my efforts seemed ______.