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

Sometimes it is based on comparatively simple drill exercises, sometimes it involves ______ challenging tasks, project or research work aimed at integrating skills and knowledge from different subject areas.