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 
No quarto parágrafo, a expressão make up em – In this case, the acid steals away electrons that make up the bond between nickel and oxygen in the ring. – é corretamente substituída por
In the text, “In addition” means
In the text, “From then on” (l.6-7) means
In “He had set up the first printing house in England in 1476”, the underlined words mean
The word that matches Kathy’s lifestyle is
In “He walks slower than I do so I must slow up.”, the underlined word means
In “… the orange has seeds and so is perpetual;…”, the transition words introduce an idea of
