From page 45 of Haskell Programming from first Principles by Christopher Allen and Julie Moronuki:

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alpha equivalence in lambda calculus 20160911_005625

Exercise

3. 𝜆𝑥𝑦𝑧.𝑧𝑥
a) 𝜆𝑥.(𝜆𝑦.(𝜆𝑧.𝑧)) 
b) 𝜆𝑡𝑜𝑠.𝑠𝑡
c) 𝜆𝑚𝑛𝑝.𝑚𝑛

Which is correct?

I believe the answer is b).

Not a) because a) omits x.

Not c) because c) should be 𝜆𝑚𝑛𝑝.𝑝𝑚 NOT𝜆𝑚𝑛𝑝.𝑚𝑛