Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:SMCIs have fast kinetics (on rate: 10(8) M 1 s (1), off rate: 100–370 s 1 (28, 29)), low pH and Mg sensitivity (28), relatively high dynamic range (FhighCa/F0Ca 1⁄4 6–40), and two-photon excitation cross sections in the range of 2–12 GM (30, 31).
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