In 1948, three American scientists invented ____ transistor, which is ____ small electronic device to control an electric current.
You may use the book as you like, _______ you keep it clean.
"Do you have any clothes to ______, Tom?" mother asked.
When will you _______ me the money that was borrowed?
I insisted that he_______ at once.
I looked everywhere in the house ______ a key that had been lost.