It shows that his quest was to learn more about the animals
A - Although he denies them, Dr. Vasequez faced several scandals last year.
A complex sentences must have both a dependent clasuse (although he denies them) and an independent clause (Dr. Vasquez faced several scandals last year.
Options B and D are compound sentences (two independent clauses) and option C is a simple sentence.
Adverbial Clause :)
This is correct, and verified by many people.
Answer: D. Adverbial Clause
