Does anyone know which the answer of the question below is?

I am confused because the answer should be (a) if the definition of “income” fluctuations means “coupon return” when think about a reinvestment risk.

But I think that the answer will be (b) if it includes “return from price changes”.

Q: Rachel Benchim is concerned about the effects of fluctuating interest rates on a fixed-income portfolio.To minimize income fluctuations, Rachel should construct a portfolio with:

(a) long duration

(b) short duration

(c) high quality issues

I got this question from a website but cannot see the answer…