Using the S&P $500$ portfolio as a proxy of the international market portfolio

Using the S&P $500$ portfolio as a proxy of the international market portfolio

is appropriate because U$.$S$.$ securities represent more than $60\%$ of world equities.

is appropriate because most U$.$S$.$ investors are primarily interested in U$.$S$.$ securities$.$

is appropriate because most U$.$S$.$ and non$-$U$.$S$.$ investors are primarily interested in U$.$S$.$ securities$.$

is inappropriate because U$.$S$.$ securities make up less than $41\%$ of world equities.

is inappropriate because the average U$.$S$.$ investor has less than $20\%$ of his or her portfolio in non$-$U$.$S$.$ equities.