By examining fossilized beetles, a research team has produced the most detailed description yet of temperatures in Britain over the past 22,000 years. Fossils of species that still exist were selected and dated. When individuals of several species found in the same place were found to date to the same period, the known temperature tolerances of the existing beetle species were used to determine the maximum summer temperature that could have existed at that place and period.
The procedure of the researchers assumes which one of the following

A．Beetles can tolerate warm weather better than cold weather.

B．Fossils of different species found in the same place belonged to different periods.

C．The process of dating is more accurate for beetles than for other organisms.

D．The highest actual summer temperature at a place and period equaled the average of the highest temperatures that could have been tolerated by each of the beetle species found there and dated to that period.

E．(E) The temperature tolerance of the beetle species did not change significantly during the 22,000-year period.