Penny measured the time that it took her rat to run through a maze. She conducted the experiment 10 times and recorded the set of data below.

Times: 67 s, 69 s, 68 s, 66 s, 78 s, 70 s, 67 s, 69 s, 68 s, 66 s

Which time is most likely an outlier?
66 s
68 s
70 s
78 s