From VOA Special English:
Germany is facing a crisis as low birth rates combine with a growing population of citizens who are living longer.
The word "combine" somehow confused me. In my view, we can use the expression "combine with" in the following forms:
<somebody> combine <something> with <something>
<something> is combined with <something>.
Of course, "low birth rates" and "a growing population of citizens" both belong to "<something>", and considering the omitted verb "is", I think maybe "combined with" is more appropriate. So, can anyone tell me why does it use "combine" instead of "combined"?