10. She ... buy two tickets yesterday. a) must b) had to c) has to

Правильный вариант: b) had to.

Слово yesterday указывает на прошедшее время. Прошедшая форма выражения have to — had to.

Ответ (English)

She had to buy two tickets yesterday.

Перевод (RU)

Ей пришлось купить два билета вчера.