The correct answer is CNAME Record.

CNAME Record is correct because a CNAME maps an alias name to a canonical host name and it is the standard way to point a custom host name or subdomain to the App Service default host name such as myapp.azurewebsites.net. App Service verifies the mapping to the platform provided host name so using a CNAME ensures the DNS name resolves to that canonical name.

A Record is incorrect because an A record maps a name to an IP address and does not point to another host name. Using an A record would require an IP address which is not the same as pointing to the App Service default host name.

TXT Record is incorrect because TXT records are used for carrying arbitrary text and verification data and they do not create an alias to the App Service hostname.

Alias record is incorrect for this question because although Azure DNS supports alias records for mapping apex domains to Azure resources, the standard and expected method to point a custom host name to the App Service default host name is to use a CNAME. Alias records are more commonly used when you must map a root domain and cannot create a CNAME at the apex.

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