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

Thanksgiving is also a national holiday. The __________________ Thanksgiving was observed by the early settlers in Massachusetts in 1629, in gratitude for their successful harvest.