What does textbook author Alan Brinkley allude to in mentioning “middle ground” in his introduction?

Alan Brinkley was an American political historian who taught for over 20 years at Columbia University. He was the Allan Nevins Professor of History until his death. From 2003 to 2009, he was University Provost.

Explanation:

frederick william of brandenburg-prussia trained his son, frederick, to be a hardy soldier. but frederick disliked rifle shooting and horseback riding. unlike his father, he was interested in french literature. he enjoyed poetry and music and, like some others of the enlightenment, he scoffed at religion. his father thought him soft, frivolous and unmindful of his duties. and when frederick refused to put his signature on a right to succession, for a few moments his father strangled him.

b is the answer i am assuming