Answer: The height, width, size, and proportions of the letters.
Step-by-step explanation:
The aspect of handwriting that relates to the size of letters is the height, width, size, and proportions of the letters. The height, width, size, and proportions of the letters are the most important features that determine the readability of the text. They must be in proportion to one another for the writing to be clear, legible, and easily readable.
Therefore, the correct answer is: The height, width, size, and proportions of the letters.