Ans: B) Time
Rate is a measure of change of a particular property over a certain time period. The property could be concentration, volume, mass etc.
Mathematically, if x denotes a certain property and t denotes the time then:
Rate = Δx/Δt = x2-x1/t2-t1
x1 and x2 are the initial and final values of the measured property measured at time t1 and t2 respectively.
Thus, rate is related to time.