Answer:

The correct answer is option 'C' - "unless he practises".

Explanation:

In this sentence, we are discussing the likelihood of someone winning a competition. The sentence structure suggests that there is a condition that needs to be met in order for the person to have a higher chance of winning. Let's break down the sentence to understand it better.

1. "He is less likely to win" - This part of the sentence establishes the probability of winning as low.
2. "unless" - This word indicates that there is a condition that needs to be fulfilled in order to increase the chances of winning.
3. "he practises" - This is the condition itself, expressing that the person needs to practice in order to improve their chances of winning.

Now, let's analyze the given options:

a) "until he practised" - The word "until" suggests a time-based condition, which is not appropriate in this context. Moreover, the use of the past tense "practised" is incorrect because it implies that the person has already practiced and the action is completed, which does not align with the intended meaning.

b) "unless he practises" - This option correctly uses the present tense "practises" to indicate that the person needs to practice regularly. The word "unless" also conveys the conditionality required for increasing the chances of winning.

c) "unless he practises" - This option is the same as option 'b' and is the correct answer.

d) "unless he does not practise" - This option uses a double negative construction, which creates confusion and makes the sentence unnecessarily complex. It is better to use a positive statement to express the condition.

e) "No correction required" - This option implies that the given sentence is already correct, which is not the case. The sentence requires the correct verb form for the condition.

In conclusion, option 'C' - "unless he practises" is the correct answer as it appropriately expresses the condition required for increasing the chances of winning.