Translation:What lives without a tongue, but speaks? A radio.
Havent you ever heard the term "came to life" to describe an electrical device being turned on or a natural phenomenon becoming active? Volcanos can come to life, televisions can come to life, etc. After all, life in people and animals is just complex electrical activity...
This voice makes me sick. Some words, it pronounces "А" instead of "О" while Google Translate and some native speakers pronounce "О"and they said that this voice is simply wrong. How can a teaching language app and also the best app for learning languages on Google Play and App Store hired a non-native speaker to make the voice for the course? This problem makes the learners wrong accent and hard to be fixed later.
There is no specific radio being discussed, so "a" is better, and it is also the way most riddles of this type are phrased in English (unless the answer is "the sun" or something else unique). That said, I agree "the" should be accepted, because it shows you understood the Russian.