As sales of digital cameras increase, so do sales of photo printers. What factor is affecting demand?

John has to choose between two jobs: one that offers him $50 per hour and one that offers him $35 per hour. The opportunity cost of choosing the job that offers him $50 per hour is:

A) $1.5 per hour. B) $15 per hour. C) $35 per hour. D) $85 per hour.

Most economists consider a theory a good one if it predicts well

a. True b. False