biodegradable[可生物降解的]

　　-eg: biodegradable garbage[可生物降解垃圾];

　　motor vehicle exhaust[汽车尾气]

　　-eg: motel vehicle exhaust leads partly to the greenhouse effect.;

　　be in short supply[供应不足]/shortage/scarcity/lack of

　　-eg: petrol is in short supply.