Oracle database: want to check privileges that I gave to the users

I create some users (c##U100, c##U101, c##U102, c##U103, c##U104) to practice grant privilege command, and my authorization graph is as follow: authorization

my professor asks me to test the privileges using those commands:

col owner format a20
col table_name format a15
col privilege format a10
col grantee format a10

SELECT owner,privilege,table_name,grantee
  FROM sys.dba_tab_privs
 WHERE grantee like 'c##U1%'
 ORDER BY grantee, table_name, privilege;

But it doesn't work, it returns "No rows selected". Kind of wondering if there's something wrong with my previous steps or with this piece of code... Thank you!

User names are always in upper case; capitalize the 'c' in your query.

SELECT owner,privilege,table_name,grantee
  FROM sys.dba_tab_privs
 WHERE grantee like 'C##U1%'
 ORDER BY grantee, table_name, privilege;