To solve this problem, we need to understand the sliding filament theory, which explains muscle contraction. Let's analyze the options:$\newline \bullet$Option 1: When myofilaments slide past each other, actin filaments shorten while myosin filaments do not shorten.$\newline$ - This is incorrect because neither actin nor myosin filaments shorten during muscle contraction.$\newline \bullet$Option 2: Actin and myosin filaments shorten and slide past each other.$\newline$ - This is incorrect because the filaments do not shorten; they only slide past each other.$\newline \bullet$Option 3: Actin and myosin filaments do not shorten but rather slide past each other.$\newline$ - This is correct. During muscle contraction, the actin and myosin filaments slide past each other, causing the sarcomere to shorten without the filaments themselves shortening.$\newline \bullet$Option 4: When myofilaments slide past each other, myosin filaments shorten while actin filaments do not shorten.$\newline$ - This is incorrect because neither filament shortens during contraction.$\newline$Therefore, the correct explanation of the sliding filament theory is given by Option 3.