Final answer:
The plural form of 'prognosis' is 'prognoses', following the rule for pluralizing Greek-derived nouns that end with '-is', which change to '-es'.
Step-by-step explanation:
The plural form of prognosis is prognoses. In English, many words of Greek origin follow specific rules for pluralization. Instead of adding an 's' or 'es' as you might in regular English nouns, words ending in '-is' often change to '-es' to form a plural. This is why 'prognosis' becomes 'prognoses' when talking about more than one. Another example is the transformation of 'diagnosis' into 'diagnoses' in its plural form. It's important when writing or speaking to use the correct plural forms to maintain professional and clear communication.