[求助]请帮忙看一下！OG-140没问过的部分-->leonchan转移 - ChaseDream

140. Declining values for farm equipment and land, the collateral against which farmers borrow to get through the harvest season, is going to force many lenders to tighten or deny credit this spring.
(A) the collateral against which farmers borrow to get through the harvest season, is
(B) which farmers use as collateral to borrow against to get through the harvest season, is
(C) the collateral which is borrowed against by farmers to get through the harvest season, is
(D) which farmers use as collateral to borrow against to get through the harvest season, are
(E) the collateral against which farmers borrow to get through the harvest season, are
What does it mean by "the collateral against which farmers borrow to get through the harvest season? I don't understand this clause. Can anybody help?

请问关于这一题，collateral应该是作为declining values 的同位语八？那为什么不用复数形式呢？