英语语法：分不清分词状语

英语语法：分不清分词状语我今天问了一个这样的问题Asia,and North America.The Antarctic is a continent almost as large as Europe and Australia combined,centered roughly on the South Pole and surrounded by the most unobstructed water areas of the world -- the Atlantic,Pacific,and Indian Oceans.我问的是centered on 在这个句子里面是不是作动词,因为我感觉centered roughly on the South Pole and surrounded by the most unobstructed water areas of the world -- the Atlantic,Pacific,and Indian Oceans.前面省略了主语The Antarctic 也就是is 和centered on 是并且谓语,但是今天又一个高手告诉我说这个是做非谓语.我有时候真分不清啊,我看见动词总是相当然认为动词前面缺少主语,然后就把动词当成谓语了.