Sally and Maria hypothesized that earthworms lived only in dark, damp places. They measured a one-meter square in a shady spot near a stream. They dug through the soil and collected earthworms. They collected 43 worms. They repeated the experiment in several locations, sunny and dry included. They found the most worms in the shady, damp plot near the stream. Several other groups of science students carried out the same experiment and got similar results. This is an example of
A) bias.
B) repetition.
C) replication.
D) validity.