Can you please help me with this question?

Portfolio Yield is most accurately measured by:

a)Using the weighted average yield of the market value of bonds in the portfolio.

b)Measuring and aggregating the cash flows for each individual bond, and calculating yield relative to the present market value of the combined portfolio.

c)Summing the YTM's for all bonds in the portfolio, and dividing by the number of holdings in the portfolio.

d)None of the above.