You have an Azure Active Directory (Azure AD) tenant named contoso.com. All users who run applications registered in Azure AD are subject to conditional access policies. You need to prevent the users from using legacy authentication. What should you include in the conditional access policies to filter out legacy authentication attempts? 

Answer options:

A. a cloud apps or actions condition
B. a user risk condition
C. a client apps condition
D. a sign-in risk condition

C

Reference: https://docs.microsoft.com/en-us/azure/active-directory/conditional-access/block-legacy-authentication