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32 Mohammad Mahfooz HussainExplanation:The phrase %u201chas been being developed%u201d is grammatically correct but is considered awkward and is seldom used in standard English. Instead use Present Perfect Passive + time phrase.3. Past Perfect Continuous Tense:Syntax:Active Subject + had + been + Ving + ObjectPassive Subject + had + been + being + V3 + ObjectAlternative Past Perfect Passive (with time phrase)Example:Active: The researchers had been conducting experiments for several months.Passive: Experiments had been being conducted by the researchers for several months.Alternative: Experiments had been underway by the researchers for several months.Explanation:Similar to the previous cases, %u201chad been being conducted%u201d is grammatically feasible but is awkward and rarely used. Instead use Past Perfect Passive + Time Phrase.