You have a requirement in your application to group faces based on the similar looking faces.Assuming that you have initialized the variables, authorized the API call, created the PersonGroup and created the persons for the PersonGroup. Review the code snippet given below for adding faces to the persons and complete it by choosing the most appropriate answer choice: 
<pre class="brush:java;">Parallel.For(0, PersonCount, async i =&gt;
{
Guid personId = persons[i].PersonId;
string personImageDir = @"/path/to/person/i/images";
foreach (string imagePath in Directory.GetFiles(personImageDir, "*.jpg"))
{
await WaitCallLimitPerSecondAsync();
using (Stream stream = File.OpenRead(imagePath))
{
await faceClient………………………………………………………….(personGroupId, personId, stream);
}}
});
</pre> 

Answer options:

A.PersonGroupPerson.AddFaceFromUrlAsync
B.PersonGroupPerson.CreateAsync
C.PersonGroupPerson.UpdateFaceAsync
D.PersonGroupPerson.AddFaceFromStreamAsync

Correct Answer: D
Option A is incorrect because in order to use AddFaceFromUrlAsync method, you would need to provide image urls, such as “string imageUrl = "https://<path to jpg file>";
Option B is incorrect because the CreateAsync method is used for creating the person. Here is a quick example “persons[i] = await faceClient.PersonGroupPerson.CreateAsync(personGroupId, personName)”
Option C is incorrect because the UpdateFaceAsync method is used to update a person`s persisted face data. Requirement here is to add new faces instead.
Option D is correct because the requirement here is to add faces to the PersonGroup using an stream input. Here is the completed C# code
<pre class="brush:java;">Parallel.For(0, PersonCount, async i =&gt;
{
Guid personId = persons[i].PersonId;
string personImageDir = @"/path/to/person/i/images";
foreach (string imagePath in Directory.GetFiles(personImageDir, "*.jpg"))
{
await WaitCallLimitPerSecondAsync();
using (Stream stream = File.OpenRead(imagePath))
{
await faceClient.PersonGroupPerson.AddFaceFromStreamAsync(personGroupId, personId, stream);
}}
});
</pre>
Reference:
To learn more about adding faces to a group, use the link given below: 

https://docs.microsoft.com/en-us/azure/cognitive-services/face/face-api-how-to-topics/how-to-add-faces