Most economists agree that ______ is/are the single most important source of productivity improvements.?

Question

Most economists agree that ______ is/are the single most important source of productivity improvements.

A. increases in human capital

B. increases in physical capital

C. technological advances

D. discoveries of natural resources

E. the establishment of well-defined property rights

Answer 1

You might guess C, but you'd be wrong.

A. increases in human capital

Read your textbook.

Answer 2

C.  It's the only one that makes sense.

Answer 3

Most agree with C.!!

I agree also with A.

Probably I am also a minority member, but the question was clear. However, I would say that an objective answer is not possible to make ("most"? there was any voting or a poll?). We are dealing here with subjective and reasonable opinions.