Answer :
The right answer for the question that is being asked and shown above is that: "c. They have Spanish origins and therefore have irregular plural forms." Some nouns that end in –sis are made plural by changing the –sis to –ses.
The answer is:
a. They have Greek origins and therefore have irregular plural forms.
This noun that have greek origins have irregular plural forms like analysis, its plural form is analyses, diagnosis, diagnoses. These are greek words that we use in our day to day life.