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

Believe it or not, when New York replaced many of its older subway cars in the 1950’s, some of __________________ had been in use for over 40 years.