The police say there is a $50,000 _______ for any information that helps them find the killer.

There being no witness on the spot, the police were delayed by the _____ of information about the crime.

A successful scientist needs _____ if he wants to make hypothesis (假设) of how processes work and how events take place.

The term paper was due to December 1, but hard as he tried, he was unable to meet the _____ for it.

  Lu Xun said, “ The ____ were made by people.”