You didn't ask me for help. I could have helped you! (SHOULD) --> You _____________________ me for help!
You SHOULD HAVE ASKED me for help!
My friend was late to Biology class, so we couldn't present our project on the life cycle of silkworms. (ABLE) --> My friend was late to Biology class, so we _____________________ our project on the life cycle of silkworms.
My friend was late to Biology class, so we WEREN'T ABLE TO PRESENT our project on the life cycle of silkworms.
Being a teacher can't be easy. (MUST) --> Being a teacher _____________________ .
Being a teacher MUST BE DIFFICULT.