Refer to the given flow chart and select the option which correctly identifies P, Q, R and S.
| P | Q | R | S | |
| A | Relative humidity | Wind speed | Thermo-meter | Rain gauge |
| B | Wind speed | Relative humidity | Thermometer | Psychrometer |
| C | Relative humidity | Wind speed | Psychrometer | Raingauge |
| D | Wind speed | Relative humudity | Thermometer | Rain gauge |
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