вставьте пропущенное слово словосочетание in more than 200 years the USA Constitution...26 times

Ответ на вопрос:

In more than 200 years the USA Constitution has been amended 26 times. 

Also can say has been changed. Must use Present perfect  and  also someone changed it, not constitution changed it by itself. So need write has been changed or amended. Need use passive.