An experiment was conducted to compare the mean reaction times to two types of
traffic signs: No Left Turn and Left Turn Only. Ten drivers were included in the
experiment. Each driver was presented with 40 traffic signs - 20 No Left Turn and 20
Left Turn Only - in random order. The mean reaction time to each type of sign was
recorded for each driver. So, for example, individual #1 reacted, on average, within
824 milliseconds to the No Left Turn and within 702 milliseconds to the Left Turn
Only sign. The design of this experiment most closely resembles a: