Explanation:

Let's evaluate the statements and options:

- Statement I: The train crosses a pole in 10 seconds.

- This gives us information about the time it takes for the train to pass a specific point, which can be used to calculate speed if the length is known.

- Statement II: The length of the train is 240 metres.

- This is crucial as knowing the length allows calculation of speed when combined with the time from Statement I.

- Statement III: The train crosses a platform of equal length in 20 seconds.

- Combining the train and platform length, we can find speed using time, even without the train's length alone.

Options Evaluation:

- Option 1 (I & II): Provides both time (from I) and length (from II), enabling speed calculation.

- Option 2 (II & III): Length (II) and crossing time (III) of combined lengths of train and platform allow speed computation.

- Option 3 (All I, II & III): All data provided, so speed can definitely be calculated.

- Option 4 (Only II & either I or III): Length with either I (crossing a pole) or III (crossing platform) allows for speed calculation.

Option 4 is correct as either combination works to find the speed.

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