Step 1: Identify the reporting verb and its tense.
The reporting verb here is "said", which is in the simple past tense. When the reporting verb is in the past tense, the tense of the reported speech shifts one step back (this is called backshift of tense).
Step 2: Apply backshift to the reported verb.
The direct speech uses the simple past "did it". Since the reporting verb "said" is past tense, the reported verb must shift further back to the past perfect: "did" becomes "had done".
Step 3: Change the pronoun.
In direct speech Suresh refers to himself as "I". In indirect speech, a first person pronoun that refers back to the subject of the reporting clause (Suresh) changes to the third person "he".
Step 4: Change the time expression.
Words that describe time relative to the moment of speaking also shift when a sentence is reported. "Yesterday" refers to the day before the moment Suresh spoke, so in indirect speech it becomes "the day before".
Step 5: Put the pieces together and check the options.
Combining the backshifted verb, the changed pronoun, and the changed time word gives: "Suresh said that he had done it the day before."
(A) Suresh said that I did it yesterday: Wrong, because the pronoun "I" and the time word "yesterday" are left unchanged; a reported sentence should not keep the speaker's original pronoun and time word this way.
(B) Suresh says I did it yesterday: Wrong, because it uses "says" (present tense reporting verb) even though the passage tells us Suresh "said" it, and it also keeps "I" and "yesterday" unchanged.
(C) Suresh says that he did it the day before: Wrong, because although the pronoun and time word are correctly changed, the reporting verb is wrongly changed to "says" (present tense) and the reported verb is left as simple past "did" instead of past perfect.
Final Answer:
Only option (D) keeps "said" as the reporting verb, backshifts "did" to "had done", changes "I" to "he", and changes "yesterday" to "the day before".
\[ \boxed{\text{Suresh said that he had done it the day before.}} \]