Mother's voice held a challenge of stubborn exactitude.是什么意思？

Mother's voice held a challenge of stubborn exactitude.

母亲的声调里有固执而针锋相对的挑战意味.

voice

n. 嗓音，（动词的）语态，呼声，发言权，歌唱才能；vt. 发音，表达，说出，给（一部乐曲）配上声部，给（如管风琴音管）整声；

例句
Her voice is passionate. Her eyes are ablaze.
她声音激昂，目光如火。

held

v. 拿（ hold的过去式和过去分词 ），举行，保留；

例句
His car was held up and he was abducted by four gunmen...
他的车遭遇拦劫，随后他被4名持枪歹徒劫持。

challenge

n. 挑战，盘问，质疑，怀疑；vt. 质疑，向…挑战；vi. 提出挑战，要求竞赛（或竞争），驳斥；

例句
The post will give him a powerful political base from which to challenge the Kremlin...
这个职位将给他提供一个强有力的政治基点来挑战克里姆林宫。

of

prep. 关于，属于…的，由…制成；aux. 助动词 [非标准用语、方言] =have [主用于虚拟语气]；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

stubborn

adj. 顽固的，固执的，顽强的或有决心的，坚持的，棘手的；

例句
Mick was stubborn and domineering with a very bad temper...
米克既固执又专横，脾气还很坏。

exactitude

n. 正确，精密，精确，严

例句
...the precision and exactitude of current genetic mapping.
当前遗传图谱的精确严谨