What Doctor Who episode should I start with?

What's a good episode to start watching Doctor Who with? Do I have to watch them in order to understand what's going on?

A2: Actually, each story of the show stands alone, so there is no need watching the show in order. But I have finished Doctor Who DVD because I am a big fan of the show. You could start with "An Unearthly Child," the first episode of the original series from 1963. Or "Rose", which is the first episode from when the series was revived in 2005.

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