A contusion occurs when a strong blow or repeated blows from an object struck the body, crushing the underlying muscle fibres and connective tissues without breaking the skin. 
A contusion can vary in severity depending on the object and location of the injury. For example a contusion to the brain may cause a concussion that can cause serious symptoms that require immediate medical attention
        
             
        
        
        
 I believe it’s your head since it has more friction
        
             
        
        
        
Because people throws trash into rivers and stuff and they flow down into the ocean and makes it unclean
        
             
        
        
        
a. Electroencephalogram (EEG)
b. Positron emission tomography (PET)
c. Electrical stimulation
d. Magnetic resonance imaging (MRI)
Answer:
d. Magnetic resonance imaging (MRI)
Explanation:
Magnetic resonance imaging is a type of non-invasive medical imaging technique that produces three-dimensional (3-D) images with the aid of powerful magnetic fields and gradients together with radio waves. This MRI test of the brain helps the doctor to view the brain in slices and can be used in detecting brain tumors and injury as well as other brain related problem. It is a safe and painless test.