Which of the Following Actions Will Eventually Allow for the Reaching

Which of the following actions will eventually allow for the reaching of sustainable supply chains? 

A)  Large manufacturers requiring their first tier suppliers to have environmental policies. 
B)  Large manufacturers requiring their first tier suppliers to transfer their environmental policies to their second tier suppliers. 
C)  Large manufacturers requiring their first tier suppliers to transfer their environmental policies to their second tier suppliers and for subsequent tiers to further cascade their environmental policies 
D)  Large manufacturers requiring their first tier suppliers to transfer their environmental policies to their second tier suppliers and vice versa.