¿Cuales son las empresas mas exitosas que aún usan hoja de cálculo? porfa es urgentee

David is in week 3 of his current ashford course and has a paper due by monday night at midnight. he has finished everything but the concluding paragraph. as he boots up his computer to work on it, he sees a flash across the screen and then the screen goes black. he begins to panic as he tries desperately to turn the laptop back on. david should have saved his work on what kind of portable device?