When is it an appropriate choice in writing to use the passive voice

When the subject (person or thing) performing the action is not relevant.

Explanation:

The Passive Voice when writing or speaking is used when you wish to focus the attention on the person or thing affected by the action; instead of focusing on the person or thing who/that performs the action. I hereby give you an example.  

As you can see, the second option does not include a subject/pronoun/person, and even if it were, the most remarkable there would be the letters and not the person who performed the action, whereas in the first example, it is remarkable the fact that “they” sent the letters; not you, not me. You can as well, include a name or be more specific:

for this, you need to remember something significant in your own life, for example, if you were bullied when you were younger, you can mention your memories on this and touch on how such treatment can harm other kids your age either physically or mentally. (racism, car crashes, a parent in the hospital are all very good subjects, think hard on it! )

hope i ! : )

1 - a

2 - a

3 - c

4 - b

5 - d