In the following question, a sentence is given in direct speech. Select the option that best expresses the same sentence in indirect (reported) speech. The host asked, "Did you come by train?"

Introduction / Context:
This question concerns reporting a yes or no question. The original query asks how the guest arrived, specifically whether the guest used a train. In indirect speech, we must remove the question form, add a suitable linker such as "whether" or "if", backshift the tense, and change pronouns. Understanding reported yes or no questions is essential for accurate formal writing and speaking.

Given Data / Assumptions:

• Reporting verb: "asked" already appears in the sentence.
• Direct question: "Did you come by train?"
• Auxiliary "did" forms the simple past question.
• Pronoun "you" refers to "I" from the narrator viewpoint.
• The question expects a yes or no answer about the mode of transport.

Concept / Approach:
For yes or no questions in indirect speech, we use "if" or "whether" and follow it with normal statement word order. The auxiliary "did" disappears and the main verb "come" takes the backshifted tense, usually past perfect "had come" when the reporting verb is in the past. The preposition "by" used with "train" is correct and should be retained. Pronoun "you" changes to "I" to suit the narrator perspective.

Step-by-Step Solution:
Step 1: Keep "The host asked" as the reporting clause. Step 2: Add "whether" to introduce the indirect yes or no question. Step 3: Remove the auxiliary "did" and change the verb to past perfect: "I had come". Step 4: Retain the preposition phrase "by train". Step 5: Combine into "The host asked whether I had come by train."

Verification / Alternative check:
The reported sentence now reads as a statement that indirectly represents the original question. The tense backshift from simple past "did come" to past perfect "had come" shows that the action of coming happened before the time of asking. The linker "whether" makes it clear that a yes or no answer was expected. There is no question mark because indirect questions follow statement punctuation patterns.

Why Other Options Are Wrong:
Option A uses "have come", which is present perfect and does not fit a past reporting verb. Options C and D use the phrase "in case", which has a different meaning; it is used for precaution, not for reporting a yes or no question. They also keep "have come", which is incorrect for tense. Only option B uses "whether I had come by train", which satisfies both tense and structure requirements.

Common Pitfalls:
Students sometimes keep the question word order or even attach the question mark, but indirect questions should use statement order and normal punctuation. Another common error is to choose "if" or "whether" but forget to backshift the tense. Some learners also replace prepositions or change "by train" to "on train", which is less idiomatic in standard English. Paying attention to each element in turn ensures accurate reporting.

Final Answer:
The correct reported sentence is The host asked whether I had come by train.