Step 1: Understanding the Question:
This question tests knowledge of cropping systems and their definitions.
Step 2: Detailed Explanation:
Multiple cropping refers to growing two or more crops on the same land during the same year.
It includes intercropping (growing two or more crops simultaneously on the same land) and mixed cropping.
Mono cropping (A): Growing only one crop on the land.
Sequential cropping (B): Growing crops in sequence on the same land (one after another).
Relay cropping (C): Sowing the next crop before the previous crop is harvested.
Thus, multiple cropping is the correct answer.
Step 3: Final Answer:
Thus, if two or more crops are cultivated at the same time, it is multiple cropping, which corresponds to option (D).
[0.5cm]