12. When conducting a tracer study, the following statement(s) is(are) true? (4 points) a) A dye or tracer (Rhodamine dye or sodium chloride), conservative (nonreactive) can be used b) Tracers may be added instantaneously as a spike or slug, or on a continuous basis (step increase). c) For a step addition of a dye or tracer, at time zero, the dye is added, the concentration of dye within the reactor reaches its maximum value immediately d) For a step addition of dye to complete-mix reactor, the influent mass of tracer is zero