Stage I (High stationary): high birth \& high death rates $\Rightarrow$ P.
Stage II (Early expanding): death rate declines first $\Rightarrow$ S.
Stage III (Late expanding): birth rate begins to fall $\Rightarrow$ Q.
Stage IV (Low stationary): both rates low, near-zero growth $\Rightarrow$ R.
\[
\boxed{\text{I}\!\to\!\text{P},\ \text{II}\!\to\!\text{S},\ \text{III}\!\to\!\text{Q},\ \text{IV}\!\to\!\text{R}}
\]