Final answer:
The sentence should be completed with 'Parallel' to accurately describe that sports unions have grown or succeeded in line with the general trend, neither significantly diverging nor opposing it.
Step-by-step explanation:
The correct answer to the question "Sports unions have thrived and gone__________ to the general trend." is c) Parallel. This means that sports unions have experienced growth or success in a manner that aligns or runs alongside the general trend, not diverging significantly either positively or negatively from it.
The options a) Complementary, b) Adverse, and d) Irrelevant do not correctly complete the sentence with the meaning that sports unions have experienced a similar trajectory as the general trend. 'Complementary' would suggest that they contribute to the trend in a beneficial way, 'Adverse' suggests a negative or opposite direction, and 'Irrelevant' would imply a lack of connection with the trend.