Answer:
The correct answer would be "the membranes of thylakoid and mitochondria contain the electron transport chain (ETC)".
Mitochondria is a membrane-bound cell organelle present in almost all eukaryotic cells.
The inner membrane of the mitochondria consists of an electron transport chain which is involved in the cellular respiration. The ETC of mitochondria includes four complexes; complex I to IV
Thylakoid is also a membrane-bound organelle usually present in the chloroplast.
It is the site of photosynthesis and consists of the electron transport chain. The ETC of thylakoid membrane includes photosystem II, plastoquinone, cytochrome, plastocyanin, and photosystem I.