Hi,
this one is a tough question, in which you have to catch the special meaning to tackle it.
Right out of the bat, always ready very carefully the entire sentence BEFORE to look at the answer choices. This way, you can even make an idea what is going on, AND you are not biased or fell in love with one or more of the answer choices that could be wrong and mislead you.
The question itself, in a nutshell, says the following:
In the third amendment, we find the root of the modern concept of privacy
- so it served as a basis (first blank)
BUT at the time it was conceived, on one hand, to calm down the confederalists' requests for something (the army),
- sop - a thing given or done as a concession of no great value to appease someone whose main concerns or demands are not being met.
on the other side even before it was written, it was already a controversial issue.
- moot - a debatable controverse
Hope this is clear as explanation AND complete.
Regards