Пре­об­ра­зуй­те, если это не­об­хо­ди­мо, слово EFFECTIVE так, чтобы оно грам­ма­ти­че­ски и лек­си­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

The invention of airplanes has made parachutes important. Since then, their ___________ has been proved many times.