146.
(A) this
(B) it
(C) those
(D) which  

"Meat tends to have the highest environmental impact, partially because livestock produce methane emissions through their digestive process - something called enteric fermentation - but also because most meat comes from livestock fed with crops, 146 means the environmental footprint is not just the resources used for the livestock, but also those that go into producing the feed."

中文對照： "肉類往往具有最高的環境影響，部分原因是因為家畜通過它們的消化過程產生甲烷排放 - 這被稱為腸發酵 - 但也因為大多數肉類來自於以作物為食的家畜，146 意味著環境足跡不僅僅是用於飼養家畜的資源，還包括進入飼料生產的資源。"