Working on the Oracle APEX Sample Database Application, use the $4$ database tables, shown below, to answer following questions.

a$.$ For each table, identify primary key and foreign key$($s$).$ If a table does not have a foreign key, write None.

$\backslash$table$[[$TABLE$,$PRIMARY KEY,FOREIGN KEY$($S$)],[$DEMO$\_$CUSTOMERS,,$],[$DEMO$\_$PRODUCT$\_$INFO,,$],[$DEMO$\_$ORDERS,,$],[$DEMO$\_$ORDER$\_$ITEMS,,$]]$

b$.$ Do data of the tables exhibit entity integrity and referential integrity? Explain your answer.

$4.$ Given the following CREATE TABLE statement, identify table name, column names, primary key, foreign key$($s$),$ and other constraints. How does the CREATE TABLE statement ensure entity integrity and referential integrity?