2 part multiple choice question

Hello. I need to create a two-part multiple-choice question where if the first part is answered incorrectly, the student gets o points even if the second part is correct. The questions have to be on the same slide because the student must see the first part in order to answer the second part. I have created a free form multiple select question and used a button set on the first four answer choice for part 1 and a second button set for the four answer choices on part two. I think I need to create variables and conditions for this to work. Does anyone know the easiest way to create this scenario?