Which part of speech must agree standard written English

a) Subject and verb

Explanation:

In standard English, agreement refers to how a word or words undergo inflections and changes due to a change in a word that those words are dependent upon. This change is such that the sentence or statement must grammatically be correct after such a change (s).

For example:

I. 'You are' is grammatically correct. However, should the subject change from the second person to the first person, the sentence inflects to become 'I am' - it is a grammatical blunder to have 'You am' or 'I are'.

II. 'I was' is in its correct form. However, if the subject should change from the first person singular to the third person plural, the statement can be inflected to become 'they were'. It is grammatically incorrect to say 'I were' or 'they was' - such concord does not exist in standard English grammar

This change or inflection observed in examples I & II given above is because the verb form depends on the subject and any change in the subject leads to a commensurate change in the verb used.

Based on the above explanation, it becomes apparent that Option A is the correct answer