Merge pull request #202401 from sally-baolian/patch-36

Fix a bug for silence element

Author: PRMerger5

articles/cognitive-services/Speech-Service/speech-synthesis-markup.md

@@ -392,7 +392,7 @@ Use the `mstts:silence` element to insert pauses before or after text, or betwee
 In this example, `mtts:silence` is used to add 200 ms of silence between two sentences.
 
 ```xml
-<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
+<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="http://www.w3.org/2001/mstts" xml:lang="en-US">
 <voice name="en-US-JennyNeural">
 <mstts:silence  type="Sentenceboundary" value="200ms"/>
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