The young man looked carefully at the long document, but he couldn't make __________ what it meant.
Answer Details
The correct option is "out."
In this context, the phrase "make out" means to comprehend or understand something that is difficult to read or hear. The young man looked carefully at the long document but was unable to understand what it meant. Therefore, the most appropriate option to fill the gap is "out."
The other options are not appropriate replacements for "out" in this context. "Up" means to create or produce something. "Off" means away from a particular place or position. "Through" means to complete something or to move from one end to the other.