"For Terrel and him, exploring the cave was a real adventure" is correct. When trying to figure out these types of sentences, try removing the first subject (Terrel) and seeing how it sounds.
An argumentative essay tends to be a longer essay involving independent research, and aims to make an original argument about a topic. ... An expository essay also aims to be objective, but it doesn't have to make an original argument. Rather, it aims to explain something (e.g., a process or idea) in a clear, concise way.
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The answer would most likely be (D) Primordial.
However, (C) Avant-garde, is completely legit too I suppose.
Personally I would choose (D) as my answer as it seems to make the most sense.