Fill in the blanks with the most appropriate option:-

If I had not taken the leave, the project …………. completed by now.

would have been

The correct option to fill in the blank is would have been.

The sentence is about a hypothetical situation, in which the speaker did not take a leave. The speaker is saying that if they had not taken a leave, the project would have been completed by now. The verb "would have been" is used in the past conditional tense to talk about a hypothetical situation that did not happen.

The other options are not as appropriate:

• Had been is the past perfect tense of "have been". It would be used to talk about something that happened before another event in the past. In this sentence, it would not be accurate to use the past perfect tense, as the action of taking a leave did not happen before the action of the project being completed.
• Would have is the past tense of "will have". It would be used to talk about something that will happen in the future. In this sentence, it would not be accurate to use the past tense, as the project is not being completed in the future.
• Was is the past tense of "be". It would not be accurate to use the past tense, as the project is not being completed in the past.