Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

A limitation of calculating a bond portfolio’s duration as the weighted average of the yield durations of the individual bonds that compose the portfolio is that it:
Option A:assumes a parallel shift to the yield curve.
Option B:is less accurate when the yield curve is less steeply sloped.
Option C:is not applicable to portfolios that have bonds with embedded options.

Answer: A