Concept:The preposition "from" indicates a starting point and requires an endpoint, while "for" is used to specify a duration of time.
Explanation:The underlined part (a) uses "From thirty years."
"From" is incorrect here because it needs a pair like "from ... to ..." to show the start and end.
The phrase "thirty years" is a period of time, not a starting point.
The correct preposition for a duration is "for."
For example: "for the past ten hours" or "for two years."
Thus, (a) should be "For thirty years."
Parts (b) and (c) are grammatically correct.
The corrected sentence reads: "For thirty years he has devoted himself to public affairs without taking a holiday."
No error in (b) or (c).
Answer:(a)