... Before they start using [**chemical fertilizers**], they had the ... manure" crops**] --> /[**chemical fertilizers**]
= [**chemical fertilizers**] --> /[**"green ... Negation: [**"green-manure" crops**] AND [**chemical fertilizers**]
I found the RC section in LSAT Asia to be quite difficult, initially i just skipped the bepop passage and came back to it after doing the oyster chemical protein passage. It was hard to figure out its structure.