Investigations revealed that the senior students … the juniors to throw stones at the Principal's car.

Step 1: Analyze the question The sentence says the senior students did something to the juniors that made them throw stones at the Principal's car. We need a verb meaning to urge or provoke someone to do something wrong or harmful.

Step 2: Understand each option

• A. infuriated means made very angry. It would need an object like "infuriated the juniors," but the phrase "to throw stones" doesn't fit well, since infuriate isn't followed by "to + verb" in this sense.
• B. integrated means combined or brought into a group. It doesn't fit.
• C. instigated means urged, provoked, or incited someone to take bad action. It fits perfectly, since we say "instigated someone to do something."
• D. instituted means established (a rule, system, or inquiry). It doesn't fit.

Step 3: Test the sentence "Investigations revealed that the senior students instigated the juniors to throw stones at the Principal's car." This is natural and grammatically correct, and it makes sense: the seniors pushed the juniors into the act.

Step 4: Answer The correct option is C. instigated.

Tip: Watch for similar-looking words (instigate, institute, integrate, infuriate). Link each to its meaning:

• Instigate = incite or stir up trouble (usually followed by "to + verb")
• Institute = set up or establish
• Integrate = join together
• Infuriate = make furious

Whenever you see "someone ___ others to do something bad," think instigate.