Which statement accomplishes all the required tasks?

The customers table has the following structure:
You need to write a query that does the following tasks:
1. Display the first name and tax amount of the customers. Tax is 5% of their credit limit.
2. Only those customers whose income level has a value should be considered.
3. Customers whose tax amount is null should not be considered.
Which statement accomplishes all the required tasks?
A. SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE cust_income_level IS NOT NULL AND tax_amount IS NOT NULL;
B. SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE cust_income_level IS NOT NULL AND cust_credit_limit IS NOT NULL;
C. SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers WHERE cust_income_level <> NULL AND tax_amount <> NULL;
D. SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE (cust_income_level, tax_amount) IS NOT NULL;

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