Which drawing medium have artists commonly used to create studies for their larger final artworks? A. pencil
B. chalk
C. oil

The best answer here would be pencil.
Artists use pencil to make sketches and create studies. They then use these sketches and studies to create their final larger piece. They use pencil because it's quick, can be corrected, lightweight and easy to use. Before pencils artists would make charcoal drawings but once we had pencils it made sense to use them as they aren't messy like charcoal.