Sometimes a sensitive topic may____ in conversation. [ ]

Had it not been for the invention of television, we would not be able to see things ___on all over the world. [ ]

_____ twice a year, whether it is a car or a bus, is a rule that every driver must obey in this city.

Have you finished your homework __________— Yes， I’ve __________ finished it.

Sam had to be reminded many times _____ he could calm down and focus on his work.[ ]