There is really nothing to know. All you have to use is context clues and common sense. We know some synonyms for direct are manage and handle. Indirect means not direct, right? And we can't handle or manage earth's interior (core), right? Therefore, the study of earth's interior is an example of indirect observation because we cannot directly manage it.
C. Habitat
Hope this helps.
Coal workers' pneumoconiosis (CWP), commonly known as "black lung disease," occurs when coal dust is inhaled. Over time, continued exposure to the coal dust causes scarring in the lungs, impairing your ability to breathe.
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