Unfortunately, on test day, there is not much that you can do if you come across a word you do not know outside of trying to determine its meaning from the context.
As you prepare for the test, make sure you look up the definitions of any unfamiliar words you come across. While I was studying, I kept an ongoing list of unfamiliar words as I found the act of writing out the word and its definition helped it to stick in my brain a bit better. It is also important to read as much as you can on the side as reading is one of the best ways to enhance your vocabulary.
For this particular example, questions regarding the author's stance usually provide you with five options on a spectrum:
1) Complete rejection or disapproval 2) Qualified rejection or disapproval 3) Neutrality 4) Qualified agreement or approval 5) Complete agreement or approval
We can see that answer choice (B) gives us our qualified approval. As the other three answers are about indifference or disapproval, we can safely assume that answer choice (A) is talking about unqualified or complete approval.
In this passage, the author believes that the Universal Declaration of Human Rights is a progressive document with weaknesses (lines 45 to 46). Therefore, we cannot say that the author has unbridled (or unconstrained) enthusiasm for the document, making answer choice (A) incorrect.
Hope this helps! Please let us know if you have any further questions.
