The Davis Mountains in West Texas used to be taller than they are now. Which of the following conditions most likely caused the mountains to become shorter over time? OPTIONS:
- Heat and pressure
- Soil deposition
- Rain and wind
- River formation
A: Rain and wind

During science class, students combined 1 kg of iron filings with 1 kg of sand to create a mixture. Which of the following methods would be best for separating the iron filings from the sand? OPTIONS:
- Stir the mixture into hot water to dissolve the sand.
- Strain the mixture through a paper filter to collect the sand.
- Drag a magnet through the mixture to attract the iron filings.
- Shake the mixture to cause the iron filings to settle to the bottom.
A: Drag a magnet through the mixture to attract the iron filings.

Which best explains the importance of nitrogen in the cycling of energy and matter? OPTIONS:
- Nitrogen increases protein production in plants.
- Nitrogen decreases protein production in plants.
- Nitrogen decreases the effectiveness of photosynthesis.
- Nitrogen increases the effectiveness of photosynthesis.
A: Nitrogen increases protein production in plants.

Which of these provides most of the oxygen in Earth's atmosphere? OPTIONS:
- coral reefs
- rainforest plants
- ocean phytoplankton
- continental grasslands
A:
ocean phytoplankton