Concept:The conjunction 'though' is used to join two contrasting sentences, showing that one fact exists despite the other.
Explanation:The given sentences are: 'He has been trying his level best to win.' and 'He could not succeed.'
These two ideas contrast – effort vs. failure.
'Though' must be placed at the start of the first clause to correctly indicate that despite the effort, the failure occurred.
The tense 'has been trying' (present perfect continuous) must be retained because the action started in the past and continues to the present.
Option A changes 'has been' to 'is' – incorrect tense.
Option B places 'though' in the middle, which changes the meaning to 'but' or 'because' – not suitable.
Option D uses 'had been trying' (past perfect continuous) – incorrect because the sentence does not require a past reference before another past event.
Only option C maintains the original tense and places 'though' at the beginning, correctly showing contrast.
Answer:Though he has been trying his level best to win, he could not succeed.