An educated society is a more peaceful and ________ one, in which people are less likely to ______ arms and more likely to participate in democratic processes.

The sentence seeks to convey that an educated society is peaceful and there is less chance that people will use violence to get their voice heard. For the first blank, we need an adjective to modify the noun SOCIETY and it should be parallel to the adjective PEACEFUL. PROSPEROUS () fits contextually PRECARIOUS (dangerously likely to fall or collapse) does not fit contextually and PRINCIPLE (morally correct behaviour and attitudes) is a noun. For the second blank, we need a verb/phrasal verb. TAKE UP fits contextually. If one group or country takes up arms against another, they prepare to attack and fight them. TAKE DOWN means to separate a large structure into pieces. TAKE IN means to include something. Thus, (a) is the right answer.