Final answer:
To build a medical word, use a CF before a suffix that begins with a vowel.
Step-by-step explanation:
In medical terminology, a CF (combining form) is a word part that is added to the beginning of a word to modify its meaning. When building a medical word, a CF is usually placed before a suffix that begins with a vowel. This is done to improve the pronunciation of the word and ensure that the word flows smoothly.
For example, if we have the CF 'cardi-' meaning 'heart,' and we want to add the suffix '-ology' meaning 'study of,' the word would be 'cardiology.'
Therefore, to build a medical word, a CF is used before a suffix that begins with a vowel.