Not until he left his home _____ to know how important the family was for him.[ ]

I’ll leave you a card and you can contact me when it ___ you. [ ]

You see, “Food Safety” receives thousands of Internet hits a day. —Yes, it becomes one of the _________ topics(话题) these days.

_________ to the efforts by the headmaster, I can go back to school now.

When electric cars become ______ , we’ll need to build more charging stations.