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单项选择题 The CUSTOMERS table has these columns: Which statement finds the rows in the CUSTOMERS table that do not have a postal code?（）

A、SELECT customer_id, customer_name   FROM customers   WHERE postal_code CONTAINS NULL;

B、SELECT customer_id, customer_name   FROM customers   WHERE postal_code = '________';

C、SELECT customer_id, customer_name   FROM customers   WHERE postal_code IS NULL;

D、SELECT customer_id, customer_name   FROM customers   WHERE postal code IS NVL;

E、SELECT customer_id, customer_name   FROM customers   WHERE postal_code = NULL;

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