Trabajar means: to work
Since it's your friend that works in a restaurant, you conjugate it to él/ella/ud.
Mi amiga <em>trabaja</em> en un restaurante.
Celia Cruz fue una cantante famosisima de salsa y la musica de su pais
(it's one of the causes of the lack of energy)
los tecnologia es un causas de la falta de energia
For the first one, it's b) les
For the second one, it's a) le
