By serving others, a person focuses on someone other than himself or herself, __________ can be very eye-opening and rewarding.
The window is never opened ____ in summer.
Nobody knows it ____ me.
I don' t think Xiao Li is ____ the other students ____ mathematics.
_____ hearing the news, I was wild ____ joy.
My father began to work ____ a bus driver when he was twenty years old.