A. tm = (Δt1 - Δt2)/ loge (Δt1/Δt2)
B. tm = loge (Δt1/Δt2)/ (Δt1 - Δt2)
C. tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2)
D. tm = loge (Δt1 - Δt2)/ Δt1/Δt2
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