SHOULD : DEBERIAS,DEBERIA,DEBERIAN,DEBERIAMOS
NEGATIVE FORM: SHOULD NOT - SHOULDN'T
EXAMPLES:
SHOULD YOU STUDY YOUR LESSONS EVERYDAY ?

YES, I SHOULD / NO, I SHOULDN'T
WHAT SHOULD THE STUDENTS DO AT SCHOOL?

THEY SHOULD PRACTICE THE LESSONS
THEY OUGHT TO PRACTICE THE LESSONS
NOTE: YOU CAN USE OUGHT TO TO RESPOND QUESTIONS IN AFFIRMATIVE FORM.

MUST : DEBO , DEBES, DEBE, DEBEMOS,DEBEN
NEGATIVE FORM: MUSTN'T - MUST NOT

EXAMPLES:
WHEN MUST MARY FINISH HER TASK ?

SHE MUST FINISH IT AS SOON AS SHE CAN

WE MUSTN'T THROW PAPERS ON THE FLOOR