Answer: The right answers are:
1. Mí / ti.
2. Contigo.
3. Ti / ti.
4. Tú / yo / ellos.
Explanation: Just to elaborate a little on the answers, it can be added that this exercise is asking you to fill out the blank with the correct personal pronoun. In option 1 the speaker has asked his/her interlocutor: "Did they talk about ME? And the interlocutor has replied: "We talked about many things, but they did not say anything about YOU." You wouldn't use the pronouns yo or tú here, but mí and ti—since there is a preposition that precedes them and they refer to the speakers. Likewise, you wouldn't use the possessive adjectives mi/ ti (mine/your). In option 2 the speaker has asked his/her interlocutor: "Are you coming to the mall?" And the other speaker has replied: "No, I can't go with YOU." You wouldn't use mi (mine), para ti (for you) or mí (to me, of me, for me) here. In option 3 the speaker has said: "I can't live without YOU." And the interlocutor has replied: "And I want to live my life devoted to YOU." In both instances you would use the personal pronoun ti, since it is preceded by a preposition and it is referring to the speaker. Finally, in option 4, the two first blanks need to be filled out with personal pronouns in nominative case, and the last blank requires the use of the pronoun in objective form, since it is preceded by a preposition: "Between YOU and I, I think that my parents [...] Perhaps marriage is not for THEM."