11. What is the minimum clear opening of hatches or manholes through the length and breath of the space?

A. Less than 600 mm at height of more than 600 mm from the bottom
B. Not less than 600 mmm at height of not more than 600 mm from the bottom
C. Less than 600 mm by 800 mm at height of not more than 600 mm from the bottom
D. Not less than 600 mm by 800 mm at the height of not more than 600 mm from the bottom