Rule reminder
To form a cleft sentence: (1) Identify the element to focus. (2) Move it after 'è/sono'. (3) Connect with 'che' (or 'a + infinitive' for subject emphasis in past). (4) Keep the rest of the original sentence as the subordinate clause. (5) Check agreement of 'essere' with the focused element. Remember: the verb in the subordinate clause stays in the same tense and form as in the original.
Original: 'Ho comprato questo libro a Milano.' Emphasise 'a Milano'.