Correct Answer: Rose : Flower

Solution : Given:
Wheat : Grain :: ? : ?

Wheat is a variety of grains.

Let's check the options –
First option: Rose : Flower; Rose belongs to the category of flowers.
Second option: Boy : Girl; Both the words boy and girl specify a gender.
Third option: Clock : Clock Hands; Clock Hands is the part of a clock.
Fourth option: Body : Skin; Skin is the largest organ in the body.

So, only the first option follows the same pattern as followed by the given pair of words. Hence, the first option is correct.