Explanation
You cannot use the Snowflake web interface to create users with no passwords or remove pass-words from existing users. You must use CREATE USER or ALTER USER command instead.
Also If you create a user with no password (or alter an existing user and remove their password), this effectively disables Snowflake authentication for the user. Without a password in Snowflake, a user cannot log in using Snowflake authentication and must use federated authentication instead.

Explanation
Both Option A & B are correct.
For Refreshing External Table Metadata on a Auto Mode, John can use the AUTO_REFRESH pa-rameter properties of External table.When an external table is created, the AUTO_REFRESH pa-rameter is set to TRUE by default.
When an external table is created, the AUTO_REFRESH parameter is set to TRUE by default.
Snowflake recommend that you accept this default value for external tables that reference data files in either Amazon S3 or Microsoft Azure stages.
However, the automatic refresh option is not available currently for external tables that reference Google Cloud Storage stages.
For these external tables, manually refreshing the metadata on a schedule can be useful.
The following example refreshes the metadata for an external table named snowdb.snowschema.snow_ext_table (using ALTER EXTERNAL TABLE ... REFRESH) on a schedule.
-- Create a task that executes an ALTER EXTERNAL TABLE ... REFRESH statement every 5 minutes.
1.CREATE TASK snow_ext_table_refresh_task
2.WAREHOUSE=mywh
3.SCHEDULE='5 minutes'
4.AS
5.ALTER EXTERNAL TABLE snowmydb.snowmyschema.snow_ext_table REFRESH;

Explanation
execute SHOW STREAMS command.
Column Name: STALE_AFTER
Timestamp when the stream became stale or may become stale if not consumed. The value is calcu-lated by adding the retention period for the source table (i.e. the larger of the DA-TA_RETENTION_TIME_IN_DAYS or MAX_DATA_EXTENSION_TIME_IN_DAYS parame-ter setting) to the last time the stream was read.