Option 1 suggests that both statements are true and that reason (R) explains assertion (A). However, while (R) may partially explain why the USA became a significant source for India, it doesn`t fully explain the entirety of India`s imports, not all of which pertained to defense needs.

Option 2 also posits that both statements are true, but separates them, indicating that (R) doesn`t explain why the USA re-emerged as India`s main import source (A). This assumes a broader range of import needs beyond defense, which (R) doesn`t address.

Option 3 asserts that while the USA did re-emerge as India`s leading import source (A), the reasoning provided (R) is not correct, likely because defense imports alone wouldn`t account for the USA`s standing in Indian imports.

Option 4 suggests a contradiction wherein the USA did not re-emerge as India`s prime import source (A), but that India did increasingly rely on US defense imports (R).

The correct answer is Option 3 as the USA indeed re-emerged as India`s main import source but not mainly due to defense requirements as suggested by (R).