Translation of "Advocate" in Chinese

I'm just playing the devil's advocate.

我在给魔鬼当辩护士。

China is an advocate for the Diaoyu Islands' sovereignty.

中国主张钓鱼岛的主权。

More and more environmentalists advocate and use environmentally friendly unleaded petrol in cars.

越来越多的环保者开始宣传和使用环保的无铅汽油的汽车。

And a fierce advocate for the independence of Tibet, which the Chinese government denies.

并且倡导西藏独立，而中国政府强烈反对。