REST api, best praxis question

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REST

Dear experts
I'm very new with REST and reading a lot about it. At the moment I have a trivial question.
Lets say we have the entity "suppliers"

suppliers
  SupplierId
  SupplierName
  ...

To retrive a list of suppliers the REST api supports

GET /suppliers

Now, to retrive a specific supplier I see two possibilites:

a.) GET /suppliers/{Id}
b.) GET /suppliers?Id={Id}

My impression is that usually one will use a.) therefore my question: What are the arguments not to use b.) ?

Thank you very much in advance for some hints.

What I have tried:

Reading a lot about REST................