Must или had to?

l forgot to phone Sam yesterday. I _ phone him today
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I forgot to phone Sam yesterday. I MUST phone him today.

had to используется в времени, а так как у нас указано настоящее [today], то тут подходит только must.

hi!

i have got  your letter! i was glad to hear from you again! thankyou for your invitation. but i am compelled to upset you, i can't go with you to the concert because of my parents who are going  to the cinema at the same time and i have to stay with my little brother. next week i wiil be free and we will be able go to another concert. thanks for understanding!  

yours,

nina

вроде так:

he will not write 10 stories on tuesday.he will not see russia for the environment.it will not be able to send 200 cards on thursday.he will not make 99 large cakes on sunday.