Actually, it's a problem for normal languages as well.
As somebody else on Duolingo pointed out; in English, a singer sings and a painter paints, but a finger doesn't fing.
Yes, in this case arising from Zamenhof's aim to include recognizable words (German: Spiegel) Also *speg is not a root in itself as far as I can tell
Good job translator XD
A police stops a blonde conductor and asks for her driving force. She asks: "What is this driving force?" "It's the document in which you have your photo." The blond girl looks for in the bag and finds a spider. She looks in it and thinks that it might be that. So she gives it to him, he looks into it and indulgently says: "You could immediately say that you also belong to police."
It might be - report it. Though my English-Esperanto dictionary gives "oportuna, faciluza" as a translations for "handy".