The bus driver smelt a rat when an unregistered vehicle trailed him for several kilometers. This means that…

Step 1: Analyze the question The question tests your knowledge of idioms. The key expression is "smelt a rat," and you must choose the option that best explains what the bus driver did.

Step 2: Explain the concept "To smell a rat" is an idiom meaning to suspect that something is wrong, dishonest, or dangerous, even when you have no clear proof. It has nothing to do with an actual rat or an actual smell.

Step 3: Apply it to the sentence

• An unregistered vehicle followed the bus driver for several kilometers.
• That is unusual and could signal danger, such as a robbery or kidnapping attempt.
• So the driver began to suspect that something was not right.

Step 4: Check the options

• A. Increased his speed: This is a possible reaction, but the idiom does not mean this.
• B. Became nervous: He may feel nervous, but "smelt a rat" describes suspicion, not nervousness.
• C. Became suspicious: This is the exact meaning of the idiom. ✔
• D. Alerted the passengers: Nothing in the sentence says this happened.

Answer: C. became suspicious

Exam tip: In idiom questions, find the meaning of the whole phrase rather than its individual words. Remember: smell a rat = suspect foul play. Other similar idioms are "fishy" (suspicious) and "something is afoot" (something is going on).