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To properly test a Visualforce Controller Extension in Apex, the developer must replicate the instantiation process used by the Lightning Platform at runtime. A4 controller extension is a class whose constructor is specifically defined to accept a single parameter of the type ApexPages.StandardController. 5The standard controller acts as the bridge b6etween the custom extension logic and the underlying Salesforce record (in this case, an Account).

In the provided test method, a record acet has been inserted into the database. To create the extension object, the developer must first instantiate the StandardController by passing the acet SObject record into its constructor. Once the standard controller instance (e.g., sc) is created, it is then passed into the constructor of the AccountControllerExt class. Option B is the correct implementation of this two-step pattern. Option C is incorrect because the StandardController constructor requires a full SObject record, not just an ID string. Options A and D are incorrect because extension classes do not support constructors that take an SObject or an ID directly; they specifically require the StandardController object to provide the necessary context for standard actions and fields. Following the correct pattern ensures the test accurately simulates the page execution context.

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