江苏省常州市，推行“（）”经验，把民办幼儿园改为区直属集团所有制幼儿园。

Freeing ports on a vessel with soild bulwards（）.

A.prevent stress concentration in the bulwark

B.permit easy jettison of deck cargo in an emergency

C.provide opening through the bulwarks for mooring lines

D.allow water shipped on deck to flow off rapidly