【答案解析】The predicate is the part of a sentence or clause that expresses what is said of the subject and that usually consists of a verb with or without objects, complements, or adverbial modifiers. The predicate excludes the subject itself. Therefore, if the predicate is to be emphasized, then there is applicable to insert an auxiliary verb "do (did, does)" before the predicate verb which should be changed back to its original form accordingly. For example, "I saw the accident." can be rewritten as "I did see the accident."
1) emphasis of subject: It is I who bought a book in the city yesterday.
2) emphasis of predicate: I did buy a book in the city yesterday.
3) emphasis of object: It is a book that I bought in the city yesterday.
4) emphasis of adverbial modifier (place): It is in the city that I bought a book yesterday.
5) emphasis of adverbial modifier (time): It is yesterday that I bought a book in the city.