SQL 문법 기초반 문제

다음 중 오류가 날 가능성이 가장 높은 쿼리는?

A.
SELECT customer_name, customer_grade
FROM customers_sp
WHERE customer_id IN (
SELECT o.customer_id
FROM orders_sp o
);

B.
SELECT mem_name
FROM member
WHERE height = (SELECT MAX(height) FROM member);

C.
SELECT mem_id
FROM buy
WHERE mem_id = (
SELECT mem_id
FROM buy
WHERE prod_name IN ('아이폰','맥북프로')
);

D.
SELECT prod_name
FROM buy
WHERE price >= 50 AND amount >= 1;