He _____ English for ten years by thetime he takes the examination

Responsibility for family is ________ happiness exists when you think of your parents and children

The young lady took the dress out of the package and tried it on, only ______ if it fitted her.

you can buy $20 tickets or 30 $tickets, ______ you prefer．

Despite their good service, most inns are less costly than hotels of _____ standards.