Aidez moi a faire ces exercices de conjugaison svp merci beaucoup de m'aidez

SINCE est employé pour un point de départ
FOR est employé pour une durée
les deux sont utilisés avec le present perfect simple HAVE+ ED ou participe passé 3ème colonne

a/ I have had this computer since I was a child
b/ I bought...... ago
c they have been on the phone for
d I got the idea when I was in London

traduction
I have known her for two years
they have been using this computer since thursday
they have been in the office since this morning
we have had this problem for three days