Привет! Давай решим это вместе. Вот твои ответы:
I ... understand what he was saying because he was speaking Spanish. Ответ: couldn't
The door was locked, so I ... get inside. Ответ: couldn't
Do you mind if I ... I speak to you for a moment, please? Ответ: - (оставить пустым)
Do you want anything? ... you call Greg and tell him that I ... be late? Ответ: Could, will
What shall we buy Mum for her birthday? We ... get a big box of chocolates. Ответ: shall
I've passed my exam! - Congratulations! You ... be very happy. Ответ: must
It's raining, so we ... go out tonight. ... Then we'll stay in. Ответ: could
Удачи с твоими заданиями! Если что-то непонятно, не стесняйся спрашивать.