ORGANIC

My answer is coming out to be (D), protonated double bond O then internal attack, NOW if anyone says ki bhai protonate the OH group because more stable carbocation formation, SOLUTION MAI THEY HAVE FIRST REDUCED THE ALDEHYDE USKE BAAD PROTONATE KARA HAI MY DOUBT IS JAB PROTONATE HUYA HOGA TABHI INTERNAL ATTACK SE PRODUCT D KYU NAHI BANEGA