________ like to go swimming ________ summer. 　 　[ ]

A. Children, on

B. Children, in 　　

C. A child, on

D. A child, in

腔隙性梗死是指脑深部小血管闭塞后所致软化灶内的坏死组织被清除后而遗留下小的囊腔。此腔直径在（）mm以内。