“___ we need”是主语从句,所填词又得做need的宾语只能填what,which强调在某范围之内
way是一个独特的词,后接不定式或of doing或定语从句.
关于主语从句：
that和what的选用
that和what都可引导主语从句.what除起连接作用外,还在名词性从句中充当某些成分,可作从句的主语、宾语或表语.而that在名词性从句中不充当任何成分,无词义,只起连接词作用.如：
What he wants is a book.他想要的是一本书.
That light travels in straight lines is known to all.众所周知,光线沿直线运行.