Normalement c’est :
a. had to work hard / couldn’t relax
b. Had to (devoir) ou Could (pouvoir)go to school / had to obey their master
c. Could (pouvoir) ou Had to (devoir) escape / could live freely
d. Had to use the Underground… to escape / had to disguise themselves
e. Could sing at night / could
Il me semble que c’est ça après à toi de voir could/couldn’t = pouvoir / ne pas pouvoir
Had to : devoir (faire qlq chose..)