Update define-advanced-keys.mdx (#3098)

This PR is for a very minor grammatical correction in the docs verbiage.

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docs/source/entities/define-advanced-keys.mdx

@@ -6,7 +6,7 @@ description: Learn how to define compound keys, nested key fields, and multiple
 
 Depending on your entities' fields and usage, you may need to use more advanced `@key`s.
 For example, you may need to define a [compound `@key`](#compound-keys) if multiple fields are required to uniquely identify an entity.
-If different subgraphs interact with different fields an entity, you may need to define [multiple](#multiple-keys)—and sometimes [differing](#differing-keys-across-subgraphs)—`@key`s for the entity.
+If different subgraphs interact with different fields of an entity, you may need to define [multiple](#multiple-keys)—and sometimes [differing](#differing-keys-across-subgraphs)—`@key`s for the entity.
 
 ## Compound `@key`s
 
@@ -242,4 +242,4 @@ type Query {
 
 ## Next steps
 
-If you haven't already, learn how to [contribute entity fields](./contribute-fields) to the supergraph and [reference them](./contribute-fields#referencing-an-entity-without-contributing-fields) from subgraphs that don't contribute any fields.
+If you haven't already, learn how to [contribute entity fields](./contribute-fields) to the supergraph and [reference them](./contribute-fields#referencing-an-entity-without-contributing-fields) from subgraphs that don't contribute any fields.