—I’m not sure ______there are living things on other planets or not .—Even scientists aren’t sure about it.
--- Where’s Jenny? --- I’m not sure. She ______ in the school library.
______ stones were put together in a certain way.
I am sure Cindy will be able to find the hotel. She has a pretty good ______ of direction.
The ______ of new technology is to make life easier, not to make it more difficult.
These books must belong to ______”means “These books must be ______.”