Sentence Correction

68) In order to ensure that the paint has the same colour from batch to batch, it is the job of a quality control specialist who checks small samples of paint from each batch.
(A) it is the job of a quality control specialist who checks small samples of paint from each batch
(B) it is the quality control specialist's job to check small samples of paint from each batch
(C) the quality control specialist who checks small samples of paint from each batch
(D) the quality control specialist checks small samples of paint from each batch
(E) small samples of paint from each batch are checked by the quality control specialist

I knew OA is D; However, I always get confused over the Subject Verb agreeement in case of relative clause.

For example, Option D has a relative clause WHO and the Answer explanation says there is NO Verb here because of relative clause and did observed the same for few more examples.

Can Someone explain the CONCEPT of VERBS in case of Relative Clauses.

In option C if you closely read the sentence in your mind you fill it to be incomplete, so the sentence is a fragment.

Rule with fragments in relative clause

Consider the following 2 sentences:

1) The book is lying on the table

2) The book that is lying on the table

Sentence 1: contains the subject book, the helping verb and main verb is lying

Sentence 2: that is lying on the table is a relative clause describing the position of book. We require a main verb outside this relative clause.

The book that is lying on the table is mine.

This sentence is now correct.

Here's the basic idea:

Every proper English sentence has a subject and a main verb. This isn't true of all languages, but it is true of English: this is why we say "It's raining", for instance, even though "it" is unspecified.

In answers C and D, we have a modifier ("In order to ensure ...") and a subject being modified ("the quality control specialist"). But answer C doesn't have a main verb, it has ANOTHER MODIFIER ("the quality control specialist who checks ..."). Since C doesn't have a verb taken by the subject of the sentence, it's an incomplete sentence.

Two shorter examples:

The man who does the work.
vs
The man does the work.

The first is incomplete (we have a subject and a modifier, but no verb taken by the subject), while the second is fine.