A participle has the following form: verb + -ing, and the only word in this sentence that takes that form is A, 'flying', which is the correct answer.
Answer:
-It's natural that some people are slaves
-Slaves are inferior beings
-Slavery is good for slaves
-Abolishing slavery would threaten the structure of society
Although coal, hydrocarbons, iron ore, platinum, copper, chromium, nickel, gold and other minerals have been found, they have not been in large enough quantities to exploit. The 1991 Protocol on Environmental Protection to the Antarctic Treaty also restricts a struggle for resources.