For the circuit shown in the figure, Thevenin's voltage and Thevenin's equivalent resistance atterminals $a-b$ is
- $5 \mathrm{~V}$ and $2 \; \Omega$.
- $7.5 \mathrm{~V}$ and $2.5 \; \Omega$.
- $4 \mathrm{~V}$ and $2 \; \Omega$.
- $3 \mathrm{~V}$ and $2.5 \; \Omega$.