Select the most appropriate option to fill in the blank in the sentence given below: By the end of March, I ___ doing this job for six years.

Correct option is D

The correct option is (d) will have been.

Explanation:
The time expression By the end of March indicates a future point by which an ongoing action will have been completed or will have been in progress for a specified duration. This structure calls for the Future Perfect Continuous Tense.

Grammatical Rule (English):
Future Perfect Continuous = Subject + will have been + V₁ + ing + for/since + time expression

• This tense is used to describe an action that will have been ongoing up to a specific point in the future.
• Key trigger: By + future time + duration expression (for six years) → Future Perfect Continuous

• (a) will be – Future Continuous; used for an action that will be in progress at a specific moment in the future. It does not convey the duration (for six years) as precisely as the Future Perfect Continuous.
• (b) was – Simple Past; refers to a past action. Incorrect for a future time reference.
• (c) have been – Present Perfect Continuous; refers to an action that started in the past and continues to the present. Incorrect for a future point of reference.