on the wagon

[Vladimir13]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #544 "English Slang Idioms (147)", question 8

"I wouldn't invite Randy. He quit drinking. He had a drinking problem for a while and is now on the .......... He told me that he won't go to bars anymore so I don't think that we should call him," Jessie said to his other roommates.

(a) abstinence
(b) twelve steps
(c) wagon
(d) straight path

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #544 "English Slang Idioms (147)", answer 8

"I wouldn't invite Randy. He quit drinking. He had a drinking problem for a while and is now on the wagon. He told me that he won't go to bars anymore so I don't think that we should call him," Jessie said to his other roommates.

Correct answer: (c) wagon

Your answer was: incorrect
"I wouldn't invite Randy. He quit drinking. He had a drinking problem for a while and is now on the twelve steps. He told me that he won't go to bars anymore so I don't think that we should call him," Jessie said to his other roommates.
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Hi Teachers,

Explain me, please why "on the twelve steps" is not correct (I supposed that he began treatment)?

Why "abstinence" is not correct too? Doesn't it mean not to drink alcohol?

Thank you,
Vladimir.
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My little horse must think it queer...