She taught him how to speak English?中的how to 是什么成分?为什么加to

how 和 to 不是在一起的,to 是和 speak 组成不定式 “to speak”,how 作为副词去修饰“to speak”
,English 是 to speal 的宾语.
看下面三个句子：
She taught him English.她教他英语
She taught him to speak English.她教他说英语
She taught him how to speak English.她教他如何说英语
主语—— she
谓语—— taught
宾语—— him
宾补——how to speak English （不定式短语） 其中：
to speak——不定式,English——宾语,how ——状语
,

how to speak English是不定式作宾语补足语