When stocks with the same expected return are combined into a portfolio

A、the expected return of the portfolio is less than the weighted average expected return of the stocks.;
B、the expected return of the portfolio is greater than the weighted average expected return of the stocks.;
C、the expected return of the portfolio is equal to the weighted average expected return of the stocks.;
D、there is no relationship between the expected return of the portfolio and the expected return of the stocks.