The combining form is used to create a medical term when

The word root is developed to include a vowel sound following the term to add a smoothing action to the sound of the word when applying a suffix. The result is the formation of a new term with a vowel attached (word root + vowel) called a combining form.

Explanation:

The word root is developed to include a vowel sound following the term to add a smoothing action to the sound of the word when applying a suffix.

:

breathe deeply from your lower lungs - imagine a rubber ring around your waist (your diaphragm)

breathe in and try to push the ring outwards.

breathe in through your nose and out through your nose and mouth.

explanation: