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WithKeys
--------

**Kata:** Convert each fruit name into a key/value pair of its first letter and itself, e.g.
`apple => ('a', 'apple')`

<div class="hint">
  Use <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.util.html#apache_beam.transforms.util.WithKeys">
  WithKeys</a>.
</div>
