A.FROM.sales.JOIN.customers.USING(cust_id)FULL.OUTER.JOIN.countries.USING(country_id)
B.FROM.sales.JOIN.customers.USING(cust_id)RIGHT.OUTER.JOIN.countries.USING(country_id)
C.FROM.customers.LEFTOUTER.JOIN.sales.USING(cust_id)RIGHT.OUTER.JOIN.countries.USING(country_id)
D.FROM.customers.LEFT.OUTER.JOIN.sales.USING(cust_id)LEFT.OUTER.JOIN.countries.USING(country_id)