By engaging in trade and acting in their own self interest, World War II POWs were following the economic principle of

To calculate the J-statistic you regress the

A) squared values of the TSLS residuals on all exogenous variables and the instruments. The statistic is then the number of observations times the regression R2. B) TSLS residuals on all exogenous variables and the instruments. You then multiply the homoskedasticity-only F-statistic from that regression by the number of instruments. C) OLS residuals from the reduced form on the instruments. The F-statistic from this regression is the J-statistic. D) TSLS residuals on all exogenous variables and the instruments. You then multiply the heteroskedasticity-robust F-statistic from that regression by the number of instruments.

Ex-London School of Economics student Mick Jagger sang, "You can't always get what you want, but if you try sometime, you just might find you can get what you need." Another statement of the basic economic principle expressed in this lyric is that

a. rational decisions are not always possible. b. you can allocate your resources to what gives you the highest value. c. you can create the supply to meet your own demand. d. you can maximize social welfare by making optimal decisions.