Ask what problem PIL was invented to solve. The old rule was that only a person who had personally suffered an injury could bring a case. That rule left out exactly the people who suffer the most, because they lack money, literacy and access to lawyers. PIL loosened that rule so that a letter or a petition from any concerned citizen could set the court in motion on their behalf. With that purpose fixed, weigh the two reasons.
The distinction being tested is between the aim of a legal device and a benefit somebody might loosely hope for. PIL was designed to change who may come to court, not how fast the court moves. Mixing up those two is what makes options (A) and (D) tempting.
Let's summarize:
So option (B) is the answer.