if it will be like 1110 then its sign 1 so its -ve number in 1's complement number it will be 10000110... just shift sign bit to msb of extended form ...

and in 2's number representation it will 11111110 ... as 2's complement is weighted ..so simply write sign bit in all places from msb to extra bit in extended form

(D) is the answer. Sign extension (filling the upper bits using the sign bit) is needed while increasing the number of bits for representing a number. For positive numbers, $0$ is extended and for negative numbers $1$ is extended.