Which is a correct example of using one unit as a basis in comparative measurement?

Correct answer: Comparing the proportions of the whole figure by taking head height as one unit

Comparative measurement uses one consistent visual unit to judge the relative size of several parts. In figure drawing, the head height can be treated as one unit, then the torso, legs, arms, and total figure height can be compared against it; therefore option C is correct. The paper width is unrelated to the subject, equal one-centimetre lines ignore observed proportions, and measuring only a pencil gives no figure comparison.