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All answers having "Auto option" as clue:

3 Character Answers:

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AIR



5 Character Answers:

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ADDON

ALARM

LEASE

SROOF



6 Character Answers:

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STEREO



7 Character Answers:

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SPOILER

SUNROOF



11 Character Answers:

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TINTEDGLASS



15 Character Answers:

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AIRCONDITIONING