If the cold junction is held at $0^{\circ}$, the same thermo emf V of a thermocouple varies as $V= 10 \times 10^{-6} t -\large\frac{1}{40} \times 10^{-6}t^2$, Where t is the temperature of the hot junction in $^{\circ}C$. The neutral temperature and the maximum value of thermo emf are respectively:

$\begin {array} {1 1} (a)\;200^{\circ};2\; mV & \quad (b)\;400^{\circ}C;2 \;mV \\ (c)\;100^{\circ} ; 1\; mV & \quad (d)\;20^{\circ}C; 1\; mV \end {array}$

$(d)\;20^{\circ}C; 1\; mV$