Which of the following is the reason that the metacentric height is a valid measure of only the initial stability?（）.

A.The metacenter does not remain in the same position for large angles of inclination

B.The center of gravity shift due to inclination

C.The center of gravity shifts above the metacenter as the vessel is inclined

D.The mean draft will change as the vessel is inclinded

主城区绿地系统是（）的生态空间。