The correct answer is: A. 2%
The brain is the most complex organ in the human body. It weighs about 3 pounds (1.4 kilograms) in adults, which is about 2% of the total body weight. The brain is made up of billions of nerve cells, called neurons, that communicate with each other using electrical and chemical signals. The brain controls all of the body’s functions, including movement, thought, emotion, and memory.
Option B is incorrect because the brain weighs about 2% of the total body weight, not 3%.
Option C is incorrect because the brain weighs about 2% of the total body weight, not 4%.
Option D is incorrect because the brain weighs about 2% of the total body weight, not 5%.