Explanation:

- Option 1: "The adversely rainfall has affected the inadequate crop."

- This is grammatically incorrect. Rainfall should not be described as "adversely." The adjective and subject do not align correctly.

- Option 2: "The inadequate rainfall was adversely affecting the crop."

- This option is structurally correct. It implies a continuous effect within a certain context, like a past ongoing situation.

- Option 3: "The inadequate rainfall adversely affected the crop."

- Grammatically correct. It conveys that insufficient rainfall directly harmed the crop.

- Option 4: "The inadequate crop adversely affected the rainfall."

- This is illogical. Crops don’t affect rainfall; it's usually the other way around.

Option 3 is the best choice.