An extracurricular activity group collected some waste fixative from a photography shop (the waste fixative contains a certain amount of AgNO3), and the students are going to put it in.

According to the sequence of metal activity, the metal with strong activity can replace the metal with weak activity from its salt solution, and the metal before hydrogen can react with acid to replace hydrogen. Among the reagents given in the options, iron can react with acid, while copper and silver do not react with acid. Excluding options A and C, if reagent D is AgNO3, it cannot be completely recovered.

Therefore, choose: d.