You must have left it in the car. (Ты должно быть оставил это в машине.)
She may have gotten into trouble. (Возможно, она попала в беду.)
They may have had some difficulties. (Возможно, у них были некоторые трудности.)
He could have gotten into a car accident / He might have gotten into a car accident. (Возможно, он попал в ДТП.)
They could have been outside and didn’t hear you / They might have been outside and didn’t hear you. (Возможно, они были на улице и не слышали тебя.) и т. д.