The other question about og--140

(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

The key is E but the confusion in this problem is the agreement between the subject, Declining values, and the verb, are.  In the OG's explanation, the subject is " values" . What is the declining's function in this sentence. Declining is adjective? (I can not find it out in the dictionary.)  Thanks a lot!