The table below shows the fossils found in various layers of an undisturbed rock:

fossils in rock layers
layer (from top) fossils in layer
1 a, c
2 e
3 a, d, f
4 b
5 f, c
6 d, b

which is most likely an index fossil?
a
b
d
e

"griffith's experiment discovering the "transforming principle" in pneumococcus bacteria. griffith's experiment, reported in 1928 by frederick griffith, was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation." - griffith's experiment.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.