He devoted most of his time to researching into space, believing his hard work would ______ sooner or later.

A．pay back

B．pay for

C．pay off

D．pay up

给定供应关系SPJ(供应商号，零件号，工程号，数量)，查询某工程至少用了3家供应商(包含3家)供应的零件的平均数量，并按工程号的降序排列。

SELECT工程号, (52) FROM SPJ GROUP BY工程号 (53)

ORDER BY工程号DESC;

（53）处填（）。

A．HAVING COUNT(DISTINCT(供应商号))＞2

B．Where COUNT(供应商号)＞2

C．HAVING(DISTINCT(供应商号))＞2

D．Where供应商号2