Which of the following is an edible seed? 

Mustards are edible seeds. They are in different shades of brown. They can be added to the vegetables while cooking. It has vitamin B1 and minerals such as copper and manganese. 

Rajma is also an edible seed. It is of reddish brown color. It is kidney-shaped. 

Mango seeds are very hard. They can not be consumed. 

Therefore, the correct answer is an option (D).