Correct option is A
Option (a) contains the grammatical error.
Explanation: The phrase “a second serving of the custard by” is incorrectly constructed. In active voice, it should be “the host offered a second serving”, or in passive voice, “a second serving of the custard was offered by the host”.
Corrected version: “a second serving of the custard was refused by the host” (if in passive) OR restructured appropriately.
Grammatical rule used:
✅ Passive voice: [Object] + was/were + V3 + by + [Subject]
Example: The book was read by John.
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Information Booster: Voice error usually happens when passive structure misses auxiliary verbs like “was/were”.