A student should be careful about the subject-verb agreement in the sentences. For example, go through the below conversation;

So first question, what is meant by subject verb agreement in one line;

Subjects and verbs must in line with one another in as far as singularity and plurality is concerned.  Thus, if a subject is singular, its verb must also be singular; if a subject is plural, its verb must also be plural.

There are non-essential clauses in the sentences which tend to confuse the student. For example;

Mr. Aashish, who is my cousin, come to my house late in the night.  (Incorrect)

Mr. Aashish, who is my cousin, comes to my house late in the night. (Correct)

[“Who is my cousin” is the non-essential clause]

Practice exercises:

Mona, and Vibha, who take lessons with Sandeep, is my best friend.

{Correct sentence would be “Mona, and Vibha, who take lessons with Sandeep, are my best friend. Mona and Vibha are plural nouns.}

My grandmother, who live in Tubingen, say that she can teach me riding.

{Correct sentence would be “My grandmother, who lives in Tubingen, say that she can teach me riding. “My grandmother is singular noun”.}

The cricket ground, which is next to the class rooms, are my favorite place in the school.

{Correct sentence would be “The cricket ground, which is next to the class rooms, is my favorite place in the school”. Cricket ground is a singular noun}

Sam, whose parents are teachers, share coffee with me.

{Correct sentence would be “Sam, whose parents are teachers, shares coffee with me.” Sam is singular}

The girl, who painted these pictures is known to me.

{It is the correct sentence. There is already a noun-verb agreement}