Hi,
I saw this exercise and the question asks to add or omit an 's' where appropriate.
"To sum up, as we have seen it is quite clear that using computer(-s/ __) is a double-edged sword."
One of my students said that I should add an 's' after computers because we are talking about computers in general. Yes, the plural does make it a bit more general. But you could still make a general reference by saying using a computer is a double-edged sword.
Another students said that we add an 's' because of the word 'using' is used. That's not really relevant. Ask him why he thinks it is. Ask him if he sees anything wrong with 'I wrote my essay using a computer'.
Which reason is correct? Tell them the main reason you need the plural is that you'd need the article 'a' if you left the word 'computer' as singular. In other words, you can't say using computer is a double-edged sword. The exercise doesn't indicate that you are allowed to add an 'a'.
Best wishes, Clive