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In the circuit shown below, for the MOS transistors, $\mu_{\mathrm{n}} \mathrm{C}_{\mathrm{ox}}=100 \; \mu \mathrm{A} / \mathrm{V}^2$ and the threshold voltage $\mathrm{V}_{\mathrm{T}}=1 \mathrm{~V}$. The voltage $\mathrm{V}_{\mathrm{x}}$ at the source of the upper transistor is

1. $1 \mathrm{~V}$
2. $2 \mathrm{~V}$
3. $3 \mathrm{~V}$
4. $3.67 \mathrm{~V}$