In context, which is the best transition to use at the beginning of sentence 10 (reproduced below)?
Ignorance was bliss for Douglass, who now understood exactly how terrible his situation was because he knew what was out of his reach on the other side.

This is correct because the writer uses sentence 11 to make a conclusion on what she discussed in the previous sentence, so “in a way” would work best. While subsequently has a similar connotation to “in a way,” “subsequently” is firmer and more unmoving, and doesn’t fit the tone of the paragraph.