The world’s supplies of petroleu

The world’s supplies of petroleum （）.

have gradually exhausted

are being gradually exhausted

are gradually exhausting

 are gradually exhausted

本题考察的是现在进行时的被动语态：石油正在逐渐地被消耗。exhaust是动词，消耗。主语是supplies 是复数，gradually 长期内逐渐地，慢慢地。