Answer: flat.

The **yield to maturity (YTM)** provides a good estimate for expected return when the **spot rate curve is flat**. This is because: - YTM assumes all cash flows are reinvested at the same rate (the YTM itself) - When the spot rate curve is flat, all spot rates are equal, making the reinvestment assumption valid - With upward or downward sloping curves, the reinvestment rates for different cash flows would differ from the YTM, making YTM a poor estimate of expected return In essence, YTM equals expected return only under the unrealistic assumption of a flat yield curve.

Author: LeetQuiz Editorial Team