Which one of the following is most suitable used as a filler crop in a mango orchard

Answer: Option D

Papaya is the most suitable to be used as a filler crop in a mango orchard.
Growing short-duration crops in between the newly established perennial crops for a few years to fill the space and to utilize the resources is termed filler cropping.
Short-lived trees are known as 'fillers'. Papaya is itself planted as filler in mango, litchi and guava orchards because it stays in the field for 2 - 3 years only.