Об­ра­зуй­те от слова DIFFER од­но­ко­рен­ное слово так, чтобы оно грам­ма­ти­че­ски и лек­си­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

Like the settlement of the United States, much of Australia’s history deals with the push west. There was, however, one big ______________. In their drive westward, the Australians found no rich river valleys or fertile plains. Instead, they found only dry empty land they called the outback.