The correct answer is A. Lost.

1. Lost: The phrase "a lost battle" refers to a situation where success is highly unlikely, implying that thinking Ronaldo will join Eyimba Football Club is an unrealistic expectation. "Lost" describes a battle that has already been defeated or is unlikely to be won.

2. Loose: This is an incorrect option. "Loose" means not tight or free, which does not fit the context of describing an impossible or futile situation.

3. Loss: This noun refers to the state of losing but is not used as an adjective to describe a type of battle. It doesn’t fit grammatically in the phrase.

4. Losing: The adjective "losing" could describe a battle that is currently being lost, but "lost" is more appropriate in the context of a hopeless situation or a battle that has already been considered failed.

Summary:

- A. Lost is the correct choice because it accurately conveys the idea that thinking Ronaldo will join Eyimba Football Club is like fighting a battle that is already considered a failure or unlikely to succeed.