What is the part of speech of the sum you talked to him about?

and should be prepositions in this sentence.

refers to the classification of parts of speech based on the characteristics of words.

Part of speech is a linguistic term and a grammatical classification of words in a language. It is the result of dividing words based on grammatical features (including syntactic functions and morphological changes) and taking into account lexical meanings. Words in modern Chinese can be divided into 12 parts of speech.

Grammatical features of prepositions

(1) It expresses grammatical meanings such as time, place, way and object. Such as: (from) tomorrow (indicating time), (at) home self-study (indicating place), (according to) principle (indicating way); Finish (one's homework).

(2) The subject-object structure mainly acts as an adverbial to modify verbs or adjectives. Such as "get out of the car" and "taller than him". Some guest-object structures can be used as attributes, but "de" should be added, such as "evaluation of historical figures" and "books on the table" A few guest-object structures can serve as complements, such as "working late into the night" and "sleeping in bed". The subject-object structure cannot be used as a predicate.

(3) "zai, xiang, yu, zhi, gei, zi" can be directly attached to verbs or other words to form a whole, which is equivalent to a verb. Such as "Fall on me", "Rush to the 21st century", "Depend on your test scores", "Be brave in practice", "Go to your destination", "Dedicated to the people" and "From new york".