Some of the main functions of skin cells are to provide protection, perceive and transmit sensation, control evaporation and regulate temperature.<span> Skin cells, which are epithelial cells, are also self-repairing and reproduce quickly.</span>
        
                    
             
        
        
        
Answer;
B) Neurons, epithelial cells 
Explanation;
-Primary lateral sclerosis (PLS) is a rare neuromuscular disease with slowly progressive weakness in voluntary muscle movement. PLS belongs to a group of disorders known as motor neuron diseases. PLS affects the upper motor neurons (also called corticospinal neurons) in the arms, legs, and face. 
-It occurs when nerve cells in the motor regions of the cerebral cortex (the thin layer of cells covering the brain which is responsible for most higher level mental functions) gradually degenerate, causing movements to be slow and effortful.  The disorder often affects the legs first, followed by the body, trunk, arms and hands, and, finally the bulbar muscles (muscles that control speech, swallowing, and chewing). 
 
        
                    
             
        
        
        
B. long fibres in celery
(I've done an experiment in my science class once on xylem tissue on celery)
        
             
        
        
        
<span>UV radiation has a penetration power that can go down to the dermis, when UVA, or to the deepest layer of the epidermis, when UVB. UVA and UVB are the type of radiation that's the most potentially dangerous for DNA damaging to happen. Melanin absorbs the UV rays reducing the damage that these may produce to the living cells of the dermis and deeper, just bellow these granules.</span>