Question

The plural of ‘focus’ is ‘foci’
A) Yes
B) No

Answer 1

Hint:Grammatical number is a morphological category defined by inflexion or agreement as a means of expressing quantity. Consider the following English sentences as an example:
The apple on the table is just picked.
There are two new apples on the table.
The number of apples is indicated on the noun—"apple" singular (one item) vs. "apples" plural (multiple items).

Complete answer:
By adding a -s to the end of most singular nouns, they become plural. Depending on what letter a noun ends in, there are a variety of rules for pluralization. Since irregular nouns do not obey the rules for plural nouns, they must be memorised or looked up in a dictionary.

Singular to plural follows some rule that is as given:
- By adding-es to a singular noun ending in s, x, z, ch, or sh, the plural is formed.
- By dropping the y and adding-ies, a singular noun ending in a consonant becomes plural by dropping the y and adding-ies.
- The singular and plural forms of certain nouns are the same.
- Some nouns take a plural verb and have a fixed plural form. They aren't used in the singular, or their singular sense is different.

The noun focus can be countable or uncountable.
In more general, commonly used, contexts, the plural form will be foci.

The plural form of Focus is Foci. So, Option A is the correct answer.

Note: Five Law are as follow
- When pluralized, singular words ending in "a" become "ae."
- When pluralized, singular words that end in "is" become "es."
- When pluralized, singular words ending in "on" or "um" become "a."
- When pluralized, singular words ending in "us" become "i."