What is the most common way to form the plural of a noun?

a. Add - s

b. Add - es

c. Add - ren

d. Add - ves

The most common way to form the plural of a noun is to add - s. The correct answer is option A. Adding - s is the most common, but is not generally applicable to all nouns. Other nouns need to be added with - es in order to form the plural noun such as the word "box". The plural form of the word box is boxes.