Error spotting (tense with 'since'): Identify the erroneous part (A/B/C) — mark D if correct — 'Since the attachment of airconditioned sleeping cars to all important trains, / travelling became very pleasant, / especially during the summer season. / No error.' Check present perfect vs. simple past and hyphenation.

Given data

• A. Since the attachment of airconditioned sleeping cars to all important trains,
• B. travelling became very pleasant,
• C. especially during the summer season.

Concept/Approach ('since' → present perfect)
When 'since' marks a starting point continuing to the present, the main clause should use present perfect: 'has become'. Also, compound adjective: 'air-conditioned' (hyphenated).

Correction
'Since the attachment of air-conditioned sleeping cars …, travelling has become very pleasant, especially during the summer season.'

Common pitfalls
Using simple past ('became') with a continuing situation; missing hyphens in compound modifiers.

Final Answer
B — Replace 'became' with 'has become' (and prefer 'air-conditioned').