Answer:
surrounded by two membranes
Explanation:
The nucleus is surrounded by two unit membranes. Together, the two membranes of the nucleus make the nuclear envelope. Therefore, the nucleus is said to be a double membrane-bound organelle. Likewise, chloroplast and mitochondria are also surrounded by two unit membranes and both are the double membrane-bound organelles. Like the nucleus, both chloroplast and mitochondria have their own DNA.