Step 1: Understanding the Concept:
We need a word close in meaning to "scurrilous" as it describes the "attack" in "They launched a scurrilous attack."
Step 2: Key Formula or Approach:
Break the word down by what kind of attack is being described: is it about how strong it was, how fair it was, how it turned out, or how rude it was in language? Match that quality to the closest option.
Step 3: Detailed Explanation:
A "serious" attack would be about its importance or gravity, not about the language used, so it does not capture "scurrilous".
An "unjustified" attack would be about whether it had a fair reason, which is a separate question from how rudely it was worded.
An "unsuccessful" attack describes only the outcome, saying nothing about the tone of the words.
An "insulting" attack matches "scurrilous" directly, since "scurrilous" describes language that is coarse, abusive, and aimed at damaging someone's name or reputation.
Since the word describes the manner and tone of the attack rather than its strength, fairness, or outcome, "insulting" is the option that lines up with its meaning.
Step 4: Final Answer:
"Scurrilous" means insulting or abusive, so option (b) is correct.