Subject
- Plankton1
- Plaques, plaquettes1
- Ponds1
- Population forecasting1
- Prothonotary warbler1
- Railroad cars1
- Railroad trains1
- Red-bellied woodpecker1
- Red-shouldered hawk1
- Roots1
- Rulers (Instruments)1
- Sand1
- Seedlings1
- Sewage disposal plants1
- Stop signs1
- Sun--Rising and setting1
- Tadpoles1
- Tree-rings1
- Trenches1
- Truck-mounted cranes1