很高兴为你解答.
句子有一点小错,谓语动词用are,复数形式.
解析：
what引导的主语从句做主语
（1）通常情况下,由what引导的主语从句放在句首时,其后的谓语动词,按语法一致的原则用单数.
What she said is correct.
What caused the accident is not clear.
（2）当主句中的表语是复数形式,或what从句的谓语动词及其补足语均为复数形式时,主句的谓语动词应用复数.
What he gave me are five English books.
What are used as chief building materials today are steel and concrete.
祝开心~!