For thousands of years comets have been a mystery to a

1.Have comets been a mystery to a man for thousands of years? (General question).

What has been a mystery to a man for thousands of years? (Special question).

What have comets been to a man for thousands of years? (Special question).

Have comets or have books been a mystery to a man for thousands of years? (Alternative question).

For thousands of years comets have been a mystery to a man, have not they? (Disjunctive question).

1.Is Stephen Hawking a theoretical physicist? (General question).

Who is a theoretical physicist? (Special question).

What is Stephen Hawking? (Special question).

Is Stephen Hawking a theoretical physicist or a teacher? (Alternative question).

Stephen Hawking is a theoretical physicist, is not he? (Disjunctive question).