Typical rates of sea-floor spreading are approximately 5 kilometers per year 50 centimeters per year 5 meters per year 5 centimeters per year

Option D,  5 centimeters per year

Explanation:

Sea floor spreading is defined as the rate of movement of sea floor after cracking. It is usually measured as the distance  moved per year by the broken sea floor (also called as ridge movement).  

An intermediate ridge moves at the rate of 5 to 9 cm/year while a fast ridge moves at the rate of 10 cm /year.  

Hence among the given answers the most suitable answer is option D