Task 2 - You can't use specific time words with present perfect. The tense should be past simple. "I talked to your teacher yesterday."
Hi, Lucia! Thanks for your contribution! Let me share with you that in exercise 2-a the part. "I've talked to your teacher yesterday" should in fact be in the Simple Past, since you are using YESTERDAY as a marker for specific time. Also, in exercise 2-d there's a typo and "YOUR"should drop the R and become just "YOU".