Explanation:

The correct answer is option 'B' - needn't.

Explanation:
- When we say "the train is late," it implies that there is no need to run because there is enough time to catch the train.
- The phrase "needn't" is a contraction of "need not" and is used to express that something is not necessary or required.
- In this context, it means that running is not necessary as the train is delayed.

Example:
- For example, if someone says, "You needn't hurry; the train is late," they are telling you that there is no need to run because there is enough time to catch the train.

Usage:
- "Needn't" is often used to give permission or to indicate that something is not obligatory.
- It is commonly used in situations where there is no urgency or rush.

Other Options:
a) daren't - This option is incorrect because "daren't" is used to express fear or reluctance, and it does not fit the context of the sentence.
c) may - This option is incorrect because "may" is used to express possibility or permission, but it does not fit the context of the sentence.
d) must - This option is incorrect because "must" is used to express obligation or necessity, but it does not fit the context of the sentence.

Conclusion:
- The correct answer is option 'B' - needn't, as it conveys that running is not necessary because the train is late.