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

People who study the sun, moon, planets and stars are called astronomers. Cave people were some of the __________________ astronomers.