When an investor adds international stocks to his or her U. S. stock portfolio, a. he or she needs to seek professional management because he or she doesn't have access to international investments on his or her own. b. it will have no impact on either the risk or the return of his or her portfolio. c. he or she will increase his or her expected return but must also take on more risk. d. he or she can reduce the risk of his or her portfolio. e. it will raise his or her risk relative to the risk he or she would face just holding U. S. stocks.