which of the following clause is used to define DATETIME2 columns in Temporal Table?

Temporal Table needs to have two DATETIME2 columns representing the start and end of the row’s validity period.
The row validity start time column is marked by the clause: GENERATED ALWAYS AS ROW START
The row validity end time column is marked by the clause: GENERATED ALWAYS AS ROW END
Both these row validity start/end time columns should be NOT NULL, if NOT NULL constraint is not specified for these columns Sql Server will consider them as NOT NULL.