In the fragments of the text: “they may lose the desire to master whatever task you are asking them to do” (lines 12-13) and “then you have to do more than just present lessons in the app” (lines 18-19), the verb forms in bold express the ideas, respectively, of 
In the sentence of the text: “However, if you want people to continue using the app, and use it frequently and often, then you have to do more than just present lessons in the app” (lines 17-19), the connector However can be replaced, without any change in meaning, by 
The word “Nevertheless” (l.13) expresses the idea of
The word “mandatory” (l.10) is the same as
The word “given” (l.1) expresses the same idea expressed by
The word “Unlike” (l.4) is the same as
The verb form “impair” (l.10) is synonymous with
In “because hiring and training new employees is costly” (l.6-7), the verb to hire means
Based on the text above, judge the following items.
The verb form “ensure” (l.3) could be replaced by make certain without changing the meaning of the text.
In the text above,
the adjective “one-size-fits-all” (l.5) means long-term and drastic.