For the n-channel MOS transistor shown in the figure, the threshold voltage $V_{Th}$ is $0.8$ V. Neglect channel length modulation effects. When the drain voltage $V_{D}= 1.6 V,$ the drain current $I_{D}$ was found to be $0.5$ mA. If $V_{D}$is adjusted to be $2$ V by changing the values of R and $V_{DD}$, the new value of $I_{D}$ (in mA) is
- $0.625$
- $0.75$
- $1.125$
- $1.5$