Which expression finds the number of different countries represented in the CUSTOMERS table?

The CUSTOMERS table has these columns:
CUSTOMER_ID NUMBER(4) NOT NULL
CUSTOMER_NAME VARCHAR2(100) NOT NULL
STREET_ADDRESS VARCHAR2(150)
CITY_ADDRESS VARCHAR2(50)
STATE_ADDRESS VARCHAR2(50)
PROVINCE_ADDRESS VARCHAR2(50)
COUNTRY_ADDRESS VARCHAR2(50)
POSTAL_CODE VARCHAR2(12)
CUSTOMER_PHONE VARCHAR2(20)

The CUSTOMER_ID column is the primary key for the table.
You need to determine how dispersed your customer base is. Which expression finds the number
of different countries represented in the CUSTOMERS table?

A.
COUNT(UNIQUE(UPPER(country_address)))

B.
COUNT(DISTINCT (UPPER(country_address)))

C.
COUNT DISTINCT UPPER(country_address)

D.
COUNT(UPPER(country_address))

E.
COUNT(DIFF(UPPER(country_address)))