Please choose the correct answer to the question: According to the endosymbiotic theory, double-membrane mitochondria originated as a result of some larger eukaryotic cells with flexible membranes engulfing smaller prokaryotic cells. Which of these explains where the outer layer of the double membrane of the mitochondria originated?

Answer1: the plasma membrane of the eukaryotic host Answer2: the nuclear membrane of the eukaryotic host Answer3: the ribosomes of the engulfed prokaryotic cell Answer4: the lysosomes of the engulfed prokaryotic cell

Answer format: answer1/answer2/answer3/answer4
Answer: answer1