First Principles Thinking: core idea
A is correct. The CFA Curriculum forward-rate equation is $(1+Z_A)^A(1+IFR_{A,B-A})^{B-A}=(1+Z_B)^B$. For a 2y1y, use $A=2$, $B=3$, so $(1.015)^2(1+IFR_{2,1})=(1.02)^3$. Solving gives $IFR_{2,1} \approx 0.0301 = 3.01\%$. This is the breakeven one-year reinvestment rate beginning two years from now.
Why top distractor is wrong (PDF-based misconception): B simply repeats the three-year spot rate instead of solving the forward-rate relation.
Why remaining distractor is wrong: C treats the forward rate like a simple difference between the spot rates rather than a compounded implied rate.