My younger sister can stay alone now, but she could not do it last year.
My best friend can play tennis now, but he could not do it a month ago.
Your dog can open the door itself now, but it could not do it last week.
I can sing very well now, but I could not when I was a child.
He can to cross the river now, but he could not when he was younger.
She can run very fast now, but she could not two years ago.