In winter, the diets of Japanese macaques, also known as snow monkeys, are influenced more by food availability than by food preference. Although the monkeys prefer to eat vegetation and land-dwelling invertebrates, those food sources may become unavailable because of extensive snow and ice cover. __ available, the monkeys then hunt for marine animals in any streams that have not frozen over.
Which choice completes the text so that it conforms to the conventions of Standard English?

