Step 1: Rule.
"Each of" always takes a singular verb. The correct perfect tense form is "has been."
Step 2: Checking options.
(A) is been — wrong.
(B) has been — correct.
(C) were being — plural, incorrect.
(D) are been — wrong form.
Step 3: Conclusion.
Correct answer is (B) has been.
Identify the part of the sentence that contains a grammatical error:
Each of the boys have submitted their assignment on time.