Concept:The sentence requires proper prepositions before each noun in a parallel structure.
Explanation:The error is in part (c): “in the centre or left side of the chest.”
The preposition “in” works for “the centre”, but “left side” needs a different preposition: “on”.
To fix it, we must insert “on the” before “left side”.
The corrected part becomes: “in the centre or on the left side of the chest”.
Thus, the sentence should read: “Most heart attacks involve discomfort in the centre or on the left side of the chest.”
No other parts have errors.
Answer:(c)