Scientists use several sources and methods to study the interior of Earth. From the options you've provided, the following are applicable:
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Core samples: These are obtained by drilling into the Earth and provide direct information about its composition and structure.
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Earthquakes: The study of seismic waves generated by earthquakes helps scientists understand the properties of Earth's interior.
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S waves: These are a type of seismic wave that can provide information about the Earth’s interior, particularly indicating where solid and liquid layers are located. S waves do not travel through liquids, so their behavior informs scientists about the outer core being liquid.
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Rock composition: Analysis of surface rocks and minerals helps infer conditions and processes occurring deeper in the Earth.
Earth's orbit and sea level are not directly used to study the interior of Earth.
Therefore, the sources scientists use to study the interior of the Earth from your list are:
- Core samples
- Earthquakes
- S waves
- Rock composition