Which of the following organizations may file Form 990-EZ?

a. Public charity with gross receipts of $40,000 and total assets of $550,000

b. Private foundation with gross receipts of $190,000 and total assets of $400,000

c. Public charity with gross receipts of $190,000 and total assets of $400,000

d. Private foundation with gross receipts of $400,000 and total assets of $90,000