Choose from the options given below so as to complete the sentence correctly:

I ______ on this project for months without success.

In the sentence, "I have been working on this project for months without success," the present perfect continuous tense is used to describe an action that started in the past and continues up to the present moment.

The correct form for the sentence is "I have been working on this project for months without success."

The other options are not suitable because they do not use the correct verb form or tense:

Option A: Have been worked
This option uses the past participle form "have been worked," which is incorrect for expressing ongoing actions.

Option C: Would have working
This option is not grammatically correct and lacks the proper verb form.

Option D: Had worked
This option uses the past perfect tense "had worked," which does not convey the ongoing nature of the action up to the present.

Therefore, the correct answer is Option B: Have been working.