22. A student prepared two trypsin solutions in plastic micro-centrifuge tubes (0.6 mL Eppendorf tube): 1 µg/µL and 1 ng/µL, respectively. He kept the solutions on ice and took small aliquots for activity assay at various time points. He found that the activities of both solutions dropped significantly over time. What reasons may cause the decay of enzyme activity? (A) 1 µg/µL: autolysis, 1 ng/µL: adsorption (B) 1 µg/µL: adsorption, 1 ng/µL: autolysis (C) 1 µg/µL: cleaved by other contaminated proteases, 1 ng/µL: autolysis (D) 1 µg/µL: autolysis, 1 ng/µL: cleaved by other contaminated proteases