The first alternative is correct (A).
The text talks about virus infection on a person's computer, which can be monitored from there.
That is, the passage has a specific subject whose exchange of experiences can contribute to a better understanding of the problem. In this context, the interlocutor can, for example, tell a particular experience in which he or she had to deal with a virus in his computer, giving details of what happened and how it was solved.
Proofreading marks are simple, convenient tools that you can use to edit your writing.
D) is the correct answer.
