Whether he succeeds is one of two great unknowns in investors' calculations about the company's future.

The Soviet Union is a country in which data on topics like pollution levels, crime rates and traffic fatalities are great unknowns.

How this happened is one of the great unknowns of astronomy.

It was as if there were a vast equation with many terms on each side, and yet only two great unknowns.

They're facing greater unknowns than their culture has ever dealt with before.

One of the greater unknowns paleoclimatologists face is the impact of the Pangean mountain range.

There were still a great many unknowns to account for, any one of which could pull the rug out from under them.

My people abandoned Vulcan, set out into space to confront the great unknowns.

This seems to be one of those great unknowns.

We are in an era of great unknowns.