很高興為你解答.
句子有一點(diǎn)小錯(cuò),謂語(yǔ)動(dòng)詞用are,復(fù)數(shù)形式.
解析：
what引導(dǎo)的主語(yǔ)從句做主語(yǔ)
（1）通常情況下,由what引導(dǎo)的主語(yǔ)從句放在句首時(shí),其后的謂語(yǔ)動(dòng)詞,按語(yǔ)法一致的原則用單數(shù).
What she said is correct.
What caused the accident is not clear.
（2）當(dāng)主句中的表語(yǔ)是復(fù)數(shù)形式,或what從句的謂語(yǔ)動(dòng)詞及其補(bǔ)足語(yǔ)均為復(fù)數(shù)形式時(shí),主句的謂語(yǔ)動(dòng)詞應(yīng)用復(fù)數(shù).
What he gave me are five English books.
What are used as chief building materials today are steel and concrete.
祝開(kāi)心~!