Yes, 單詞測驗:用圖片學習 is free to download, however it contains in-app purchases or subscription offerings.
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單詞測驗:用圖片學習 has several in-app purchases/subscriptions, the average in-app price is €5.99.
To get estimated revenue of 單詞測驗:用圖片學習 app and other AppStore insights you can sign up to AppTail Mobile Analytics Platform.