Complete the following sentence with a (compound) word derived from the one(s) given in bracket.
He had never really understood the（ ）of the Civil War. (bitter)
【正确答案】：BITTERNESS
【题目解析】：
本题考查常见形容词的名词形式。
空前为the所以空格处为名词。bitter为形容词，意思是苦的，痛苦的。其名词形式bitterness符合题意。
句意：他从来没有真正理解过内战的痛苦。