You are using the Azure Speech service to convert text to speech. The prerequisites are met, Speech SDK is installed and required packages are included. You are tasked to configure SpeechSynthesizer for the following use cases: Use Case 1: Output audio to a .wav file
Use Case 2: Output audio to a speaker
Use Case 3: Output audio as an in-memory stream
You configure four different variables to meet the requirements per the Use Cases given above. Var 1: using var synthesizer = new SpeechSynthesizer(speechConfig, null);
Var 2: using var synthesizer = new SpeechSynthesizer(null, audioConfig);
Var 3: using var synthesizer = new SpeechSynthesizer(speechConfig, audioConfig)
Var 4: using var synthesizer = new SpeechSynthesizer(speechConfig);
Review the Use Cases above and map them to the variables in order to meet the objective. 
 

Answer options:

A.Use Case 1: Var 3;Use Case 2: Var 2; Use Case 3: Var 1 
B.Use Case 1: Var 3;Use Case 2: Var 1; Use Case 3: Var 2
C.Use Case 1: Var 3;Use Case 2: Var 4; Use Case 3: Var 2
D.Use Case 1: Var 3;Use Case 2: Var 4; Use Case 3: Var 1

Correct Answer: D
Option A is incorrect because the SpeechConfig variable is necessary for all use cases. Hence its value cannot be null.
Option B is incorrect because to output audio directly to a speaker, you would omit the audiConfig parameter.
Option C is incorrect because the SpeechConfig variable is necessary for all use cases. Hence its value cannot be null.
Option D is correct. Here is the correct mapping of use cases and variables.
To output audio to a .wav file, use the following “using” statement:
using var synthesizer = new SpeechSynthesizer(speechConfig, audioConfig);
To output audio to a speaker, use the following “using” statement.
using var synthesizer = new SpeechSynthesizer(speechConfig);
To output audio as an in-memory stream, use the following “using” statement.
using var synthesizer = new SpeechSynthesizer(speechConfig, null);
Reference:
To learn more about synthesizing speech to a file, use the link given below: 

https://docs.microsoft.com/en-us/azure/cognitive-services/speech-service/get-started-text-to-speech?tabs=script%2Cwindowsinstall&pivots=programming-language-csharp