combined意思An area of Australia larger than France and German

是定语.
某些由过去分词转化而来的形容词通常后置
这类形容词主要有concerned(有关的),discussed(讨论过的),included(包括的),involved(牵涉到的),left(剩下的),needed(所需的)等,如：
The questions concerned/ involved have been all solved.
The problem discussed is very important.
The expenses are $200,postage included.
We had only three days left.
He took all things needed for the journey.

加起来的意思
An area of Australia larger than France and Germany combined is currently underwater.
澳洲目前水下的面积比法国和德国加起来还要大。

是定语，意思是“组合的, 结合的”
这句话的大致意思是，澳大利亚的一个比法国和德国两国面积之和还要的大的地区已经被水淹没。这里面的主语是an area 动词是is