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Choose one answer

1. AAddition of a fluorine atom to the piperidine ring at the 4-position
2. BSubstitution of the phenothiazine sulfur bridge with an oxygen atom; phenothiazines themselves retain the sulfur bridge unchanged
3. CAddition of a second benzene ring fused via a seven-membered diazepine ring
4. DReplacement of the ring nitrogen at position 10 with a carbon atom bearing a double-bond side chain
5. ERemoval of the piperazine side chain and replacement with a butyl ketone, the backbone seen in butyrophenones such as haloperidol