Which type of pencil is useful for making dark and soft lines?

Correct answer: Soft pencil

The governing concept is the relationship between graphite softness and mark value. A soft pencil contains comparatively softer graphite and deposits more material with ordinary pressure, so it produces broad, dark, and soft lines. Thus, option C is correct. A hard pencil usually makes light, sharp marks; a mechanical pencil describes the form of the tool, and a white pencil does not provide the expected dark graphite line.