Answer: abfss

The correct protocol for accessing Azure Data Lake Storage Gen2 from Azure Machine Learning is 'abfss' (Azure Blob File System Secure). This is the recommended protocol for ADLS Gen2 as it provides secure access over HTTPS. According to Microsoft documentation and the community discussion with 100% consensus and upvoted comments confirming option C, 'abfss' is the proper URI scheme. Option A ('https') is a general web protocol but not the specific ADLS Gen2 protocol. Option B ('adl') was used for ADLS Gen1 but is deprecated for Gen2. Option D ('wasbs') is for Azure Blob Storage with secure access, not specifically for ADLS Gen2.

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