If in two triangles, ABC and PQR, frac{AB}{QR} = frac{BC}{PR} = frac{CA}{PQ}, then which of the following is correct?

Matching the vertices based on the given proportional sides: side $AB$ corresponds to $QR$, $BC$ corresponds to $PR$, and $CA$ corresponds to $PQ$. Therefore, vertex $A$ corresponds to $Q$, $B$ to $R$, and $C$ to $P$. Thus, $\triangle ABC \sim \triangle QRP$, which means $\triangle PQR \sim \triangle CAB$.