From the given options, choose the one which gives the correct meaning for the expression

To smell a rat

To suspect a trick or deceit

The correct answer is option 4: To suspect a trick or deceit

The idiom to smell a rat means to suspect that something is wrong or that someone is trying to deceive you. It is often used when someone has a gut feeling that something is not right, but they cannot quite put their finger on it. In the sentence, the speaker is saying that they smell a rat, which means that they suspect that something is wrong with the situation. This is why the idiom to smell a rat is used in this context.