I called him yesterday.
He hasn't talked with him for a long time.
You have never seen a ghost.
They read this detective last summer.
I must go to school.
I must do my homework.
I must go in for sports.
I must drive carefully.
I must respect elderly people.
I mustn’t be rude.
I mustn’t feed animals in the zoo.
I mustn’t shout at school.
I mustn’t eat fatty food.
I mustn’t throw rubbish in the streets .
1. A
2. An
3. A
4. An
5. A
Если слово после артикля начинается с гласной, используется an, а если с согласной - a. Там есть несколько исключений, но, думаю, тебе пока это не нужно.
Will they play badminton in the park?