We must keep on learning if we want to keep up with the     of the changing times.

The scientists were trying to look for all possible _______ as to where this species came from.

Hardly a month goes by without ______ of another survey revealing new depths of scientific illiteracy among US citizens.

It is a pity that none of the ______ stopped ______ the poor man lying there, begging. 

The system has been designed to give students quick and easy           to the digital resources of the library.