On the north of the bank _____ the Opera House, _____ was built two hundred years ago.
Exploring _____space is exciting, yet dangerous. There is _____need for both robots and humans for space exploration.
Life is like time. Once _____, it never returns.
The company gave away 300 dictionaries to the students at the beginning of the term, and _____500 the next term.
While many believe Benjamin Franklin to have discovered electricity, recent findings seem to show _____.
— Can I smoke in this hall?— No, you can’t. If you _____, please go to the smoking room.