Final answer:
Option C, To use the waterways to boost northern trade, was NOT a reason for the Union to capture Fort Donelson and Fort Henry; these forts were targeted for strategic military advantages.
Step-by-step explanation:
The answer to the question of which of the following was NOT a reason why the Union wanted to capture Fort Donelson and Fort Henry during the Civil War is C) To use the waterways to boost northern trade. The capture of these forts was primarily for strategic military reasons.
The Union aimed A) To cut Confederate lines of communication, B) To prevent raw materials from reaching Confederate troops, and D) To deprive the Confederacy of fresh troops by controlling these key positions. Control of the waterways was important for moving troops and for conducting offensive operations, not specifically for boosting trade.