What contributed to the development of feudalism during the middle ages?

Which of the following descriptions is an example of the curtual diffusion

What stalled germany's initial invasion into france in 1914

Which source would best a historian understand the effect of the great chicago fire on families? a. a biography of a chicago family displaced by the fire b. a letter from a grandmother in new york to her family in chicago c. a newspaper editorial about families who were displaced d. an oral history dictated by an adolescent who fled the fire