**Rule: Understanding Idiomatic Expressions.** The idiom 'on one's best behaviour' means to be as polite and well-behaved as possible, often because someone important is present. Children often behave exceptionally well for their grandparents. Option (a) is the correct definition. Option (b) is the opposite. Options (c) and (d) are unrelated behaviours.

**Rule: Understanding Idiomatic Expressions.** The idiom 'a leap in the dark' refers to a risky action taken with no prior knowledge of what the result might be. Investing in a new, unproven startup is a classic example of such a risk. Option (a) is the correct definition. Option (b) is a literal interpretation. Option (c) and (d) are the opposite.

**Rule: Understanding Idiomatic Expressions.** The idiom 'in a tight spot' (or 'in a tight corner') means to be in a difficult predicament with few options. Losing a key player would certainly put a sports team in a tough position. Option (c) is the correct definition. Option (a) is a literal interpretation. Option (b) and (d) are the opposite.

**Rule: Understanding Idiomatic Expressions.** The proverb 'don't look a gift horse in the mouth' is advice not to be ungrateful when you receive a gift by questioning its value. (The age and value of a horse can be determined by its teeth). The sentence advises the person to simply be grateful. Option (b) defines the action the proverb warns against. Option (a) is the literal origin. Option (c) and (d) are different responses to a gift.

**Rule: Understanding Idiomatic Expressions.** The idiom 'the best thing since sliced bread' is a hyperbolic expression used to praise a new invention or innovation as being excellent. It suggests that the new thing is as revolutionary as the invention of pre-sliced bread was. Option (c) is the correct definition. Option (a) and (d) are the opposite. Option (b) is a literal interpretation.

**Rule: Understanding Idiomatic Expressions.** The proverb 'you can't have your cake and eat it too' means you cannot simultaneously keep something and consume it. Figuratively, it means you can't have two desirable but mutually exclusive things. Wanting to work less for the same pay is a classic example of this. Option (a) is the correct definition. Option (b) and (c) are incorrect interpretations. Option (d) is the opposite of the desire expressed in the idiom.

**Rule: Understanding Idiomatic Expressions.** The idiom 'a piece of cake' is used to describe a task or activity that is extremely easy to accomplish. For students who had studied, the exam would seem easy. Option (c) is the correct definition. Option (a) is a literal misinterpretation. Option (b) is the opposite. Option (d) is an unrelated topic.

**Rule: Understanding Idiomatic Expressions.** The idiom 'sick and tired of' is an emphatic way of saying that one is extremely annoyed or frustrated with something that has been happening for too long. 'Constant complaints' would certainly cause such a feeling. Option (b) is the correct definition. Option (a) is a literal misinterpretation. Options (c) and (d) are the opposite feelings.

**Rule: Understanding Idiomatic Expressions.** The idiom 'a tempest in a teapot' (or 'a storm in a teacup' in the UK) refers to a situation where a lot of anger or worry is generated by something that is insignificant. The phrase 'a lot of fuss over a minor issue' is a direct explanation. Option (b) is the correct definition. Option (a) is a literal interpretation. Option (c) is the opposite. Option (d) is a different kind of event.

**Rule: Understanding Idiomatic Expressions.** The idiom 'all thumbs' is used to describe a person who is physically awkward, especially with their hands, making them unable to perform delicate tasks. The image is of having only thumbs and no fingers. Option (c) is the correct definition. Option (a) is a literal misinterpretation. Options (b) and (d) are the opposite.