Correct Answer: (c) 3
Solution:The erroneous segment is part (3).
• There should be "that interact with each other" instead of "interacting with every other" in part (3) because "that" will be used as a relative pronoun and "each other" will be used for "regions".
• The grammatically correct sentence would be – The brain is composed of many different regions that interact with each other.
Hence, the correct answer is option (c).