Si Antonio estuviera en la fiesta, el hablaria con Juan.
This sentence means - If Antonio had gone to the party, he would have talked to Juan.
It is a hypothetical sentence, meaning that it didn't happen but states what could have happened had he decided to go to the party.
C. ¡No manches!
A is incorrect because it means "what's up?"
B is incorrect
D is correct because it means "okay"
Mi familia y yo FUIMOS a la taquera y comí taco de carne