(a).
| Groups | t | P |
|---|---|---|
| P, Q | 2,1697 | 0,0385 |
| P, R | 1,6055 | 0,1077 |
| P, S | 3,7151 | 0,0044 |
| Q, R | 2,6056 | 0,0146 |
| Q, S | 5,9167 | 0,0009 |
| R, S | 5,1805 | 0,002 |
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