In the case of the Hubbard Brook Experimental Forest,hydrogen ion concentration in precipitation was measured over a period of more than 40 years.Why was it important to track the concentration of hydrogen ions in precipitation over such a period of time? Why not use just a few years?

A) Tracking these data over more than 40 years was important because there was so little variation between years
B) The period of time was necessary to capture beginning and final concentrations only. The researchers were not interested in data in between these points
C) Measuring these data over more than a few years allowed researchers to track the trend in hydrogen concentration through time
D) Collecting data for a few years would have been misleading because of the year by year variation