Пре­об­ра­зуй­те, если это не­об­хо­ди­мо, слово BE так, чтобы оно грам­ма­ти­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

Was he really the first to reach the continent? The great Norwegian explorer Thor Heyerdal believed that ancient people ______ able to build boats that could cross oceans.