Fill in the blank with correct 'Modal Auxiliary' :
Passengers _____ not walk across the railway line. (Prohibition)

Question

Fill in the blank with correct 'Modal Auxiliary' : 
Passengers _____ not walk across the railway line. (Prohibition)

Accepted Answer

Passengers **must** not walk across the railway line.

**Explanation:**

*   **Why "must" is correct (Option 4):** "Must" is used to express a strong obligation or prohibition. In the context of railway safety, walking across the tracks is strictly forbidden due to the high risk of accidents. "Must not" clearly conveys this prohibition and the serious consequences of disobeying it. It emphasizes that there is no choice in the matter; it is a mandatory rule.

*   **Why the other options are incorrect:**

*   **Should (Option 1):** "Should" expresses advice or a recommendation. While it suggests that walking across the railway line is not a good idea, it doesn't convey the same level of prohibition and urgency as "must." It implies a suggestion rather than a strict rule.

*   **Can (Option 2):** "Can" expresses ability or possibility. "Passengers can not walk across the railway line" implies that they are physically unable to do so, which is not the intended meaning. The issue is not their physical ability, but the prohibition against doing so.

*   **Need (Option 3):** "Need not" expresses a lack of necessity. "Passengers need not walk across the railway line" implies that it's not necessary for them to do so, but it doesn't prohibit them from doing it. It doesn't convey the danger and the rule against crossing the tracks.

Therefore, "must" is the most appropriate modal auxiliary to express the prohibition against passengers walking across the railway line.