A simple pendulum has a time period $T_1$ When on earth's surface, and $T_2$ When taken to a height R above the earth's surface, where R is radius of earth. Then $\large\frac{T_2}{T_1}$ is

Question

$$(a)\;1 \quad (b)\;\sqrt 2 \quad (c)\; 4 \quad (d)\;2$$