He is ----to speak the truth.

选A too much后加可数名词的时候加of
too much有过于的意思 不是褒义 too much可作形容词短语来用,此时常用来修饰不可数名词,表示“太多……”、“过多……”之意.
much too和too much用法上的区别
两者结构相似,很容易混淆.它们在用法上的区别是：much too＝too,但前者语气更强；too much＝much,但前者语气更强.比较：
1.much too的用例
He drives much too fast.他开车开得太快了.
He’s much too young.他太年轻了.
The shoes are much too small for me.这鞋子我穿太小了.
90 miles an hour is much too fast.一个钟头开90 英里太快了.
2.too much的用例
There is too much rain.雨水太多了.
This soup tastes too much of salt.这汤太咸.
You’re asking too much.你要求太多.