Some great people said it was their primary school teachers

Some great people said it was their primary school teachers and their lessons＿＿they were fond of＿＿influenced their whole lives.
A.which; that B.that; which
C.which; what D.that; that
解析：此题考查定语从句和强调句型.第一个that引导定语从句,修饰先行词lessons,且在从句中作fond of的宾语；第二个that是强调句型it is/was…that…中的引导词that,被强调对象就是their primary school teachers and their lessons that they were fond of.
为什么第一个引导定语从句不能用which?