A sentence is provided in the question below with a part highlighted in bold. There may be an error in the highlighted part. The erroneous phrase can be replaced with one of the given alternatives. Choose "No improvement required" as the answer response if the sentence is correct.

The teacher gave us a piece on cake during the exam by giving us easy questions.

Correct option is A

Correct Answer: (a) a piece of cake
Explanation:
The original sentence is:
"The teacher gave us a piece on cake during the exam by giving us easy questions."
· The correct phrase is "a piece of cake," which is an idiom meaning "something very easy."
· The preposition "of" is appropriate for this idiom, and the current use of "on" is incorrect.
Why the other options are incorrect:
· (b) a piece to the cake: Incorrect, as "to the cake" does not fit the idiom or context.
· (c) a piece from the cake: Incorrect, as it suggests a literal piece of cake, which is not intended here.
· (d) a piece through cake: Incorrect, as it is grammatically and contextually irrelevant.
· (e) No improvement required: Incorrect, as "a piece on cake" is grammatically and idiomatically incorrect.
Thus, the correct replacement is "a piece of cake".