b) deemphasize the subject
"A car struck the pedestrian early Friday evening."
In the active voice the subject, in this case "a car", is the main focus of the sentence.
--------- --------- --------- --------- --------- ---------
"The pedestrian was struck by a car early Friday evening."
In the passive voice the object, the thing that gets acted upon (the pedestrian), is the main focus. The subject, a car, is deemphasized in the passive voice.
A passive verb is the better choice if you wish to:
A - emphasize the subject and D - establish a formal tone. Both are correct.
In passive sentences, the thing receiving the action is the subject of the sentence and the thing doing the action is optionally included near the end of the sentence. You can use the passive form if you think that the thing receiving the action is more important or should be emphasized. You can also use the passive form if you do not know who is doing the action or if you do not want to mention who is doing the action. Passive verbs use a linking verb alongside the main verb.
For example the active present perfect verb form would be found here -
Many students attended the prom. where "many students" is the subject emphasized.
Now the passive present perfect verb form would be -
The prom was attended by many students. where "the prom" is the subject emphasized.
Establishing a formal tone -
Passive verbs are common in formal writing, such as academic, technical and business papers for the following reasons -
1 - The passive voice sounds more objective.
2 - Using "I" or "We" sounds unprofessional.
3 - The passive voice emphasizes results.