Об­ра­зуй­те от слова FREQUENT од­но­ко­рен­ное слово так, чтобы оно грам­ма­ти­че­ски и лек­си­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

Ivan Tsvetaev, father of the famous Russian poet Marina Tsvetaeva, was a professor of History of Art at Moscow University. When he taught his students, he _________________ regretted not being able to show them the original antique and renaissance sculptures he spoke about.