The answers are: a. exposition, b. climax and d. falling action.
Exposition, climax and falling action are part of the basic plot structure. Plot is a sequence of events, it refers to a conflict, and it's also the main part of a story.
Exposition: the beginning of the story and introduction of the conflict.
Climax: it's the turning point of the story.
Falling action: when events begin to resolve and the story works toward its end.