Which of the following often involves positive external benefits?

Firms exist because of

A) incomplete contracts. B) team production. C) the incentive to free ride. D) all of these choices.

Last year, Casey grew fresh vegetables, which she sold at her local farmers market, but this year, Casey did not plant any vegetables and went to work at a bank instead. Which of the following best explains Casey's career change?

A. Casey's opportunity costs of gardening exceeded Casey's opportunity costs of working at the bank. B. Casey's opportunity costs of working at the bank exceeded Casey's benefits from gardening. C. Casey's opportunity costs of gardening exceeded Casey's benefits from working at the bank. D. Casey's opportunity costs of working at the bank exceeded Casey's opportunity costs of gardening.