Perseverance is a kind of quality—and that’s _____ it takes

答案是A------WHAT.
WHAT==SOMETHING THAT
it是形式主语.to do anything well是真正主语.what做表语从句部分的宾语.
1 and that’s what it takes to do anything well.----what it takes to do anything well----在is后面就是表语从句
2 what （宾语）it（形式主语） takes（谓语--需要,要求） to do anything well（真正主语）