"It's a time machine," Donna said, realising exactly what was going on.
"It's a time machine," Rose echoed, a smile beaming across her face. She remembered the familial rush she had felt as she was told the TARDIS was a time machine - now someone else experienced that pleasure. Someone much more deserving than the former shop girl, someone who was gutsy, wouldn't take no for an answer and would do the right thing. Rose now knew why the Doctor had chosen Donna. After all, he only took the best.