Your answer would be D. The possible combinations of alleles in offspring based on the parents genetic makeup. The punnet square is basically used to determine what the outcome of an offspring would be.
 
        
             
        
        
        
Contractile proteins<span> generate force for muscle contraction. The two </span>contractile proteins<span> in myofibrils are actin (part of the thin filament) and myosin (part of the thick filament)</span>