The torque-speed characteristics of motor $(TM)$ and load $(TL)$ for two cases are shown in the figures $(a)$ and $(b)$. The load torque is equal to motor torque at points $P$, $Q$, $R$ and $S$

The stable operating points are

1. $P$ and $R$
2. $P$ and $S$
3. $Q$ and $R$
4. $Q$ and $S$

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