There are a number of theories on what happened to it.

A number of theories have been advanced for the Soviet action.

No one really knows why, although there are any number of theories.

Recent research, however, has produced a number of theories about the brain and music.

A number of theories on the matter have been proposed.

A number of theories developed regarding state development in Europe.

There are a number of theories around why the village got its name.

There are a number of theories on how the village got its name.

A number of theories have been advanced to explain this.

There are a number of theories as to why this is the case.