Correct Answer & Explanation
Option C
• The sentence indicates an action that started in the past ('yesterday since morning') and continued for a period up to another point in the past (implied context).
• The presence of 'since morning yesterday' (a time expression) with a continuous action points to a Perfect Continuous Tense.
• Since the entire context is in the past ('yesterday'), the Past Perfect Continuous Tense (had been + V1-ing) is appropriate.
• 'Has been searching' would be Present Perfect Continuous, which is incorrect for an action entirely in the past.