完全可以.
When compared with the size of the whole earth是When the biggest ocean is compared with the size of the whole earth的一个省略形式,这种省略往往要求从句的主语与主句主语一致并且从句的谓语动词是 am/is/are/was/were中的一个.又如：If (he was) asked about his daughter,Mr Black would just say that she was on holiday.