Explanation:

Here’s the thing—let’s break down the options:

- The original phrase "has been attacking" is wrong because "gangs" is plural, so it should be "have," not "has."

- Option 1: No substitution required. Not right, because as I said, "has" doesn't match the plural subject.

- Option 2: "Was attacking" makes it sound like it happened only in the past, but the warning is about ongoing attacks.

- Option 3: "Have been attacking" is the sweet spot. "Gangs" is plural, and this tense shows gangs started attacking in the past and it's still happening now.

- Option 4: "Was being attacked" flips the meaning—the sentence is about gangs attacking, not being attacked.

So, Option 3—have been attacking—is correct.