Step 1: Subject-Verb agreement.
The subject "Ramesh and Radha" is plural, so the verb must be plural.
Step 2: Checking options.
(A) is — singular, wrong.
(B) was — past tense, but sentence is present.
(C) are — correct plural present.
(D) where — incorrect word.
Step 3: Conclusion.
Correct answer is (C) are.
Identify the part of the sentence that contains a grammatical error:
Each of the boys have submitted their assignment on time.