**Rule: Understanding Idiomatic Expressions.** The proverb 'you can't judge a book by its cover' is a metaphor that means one should not prejudge the worth or value of something or someone by their outward appearance alone. The sentence uses this to caution against trusting someone just because they 'seem friendly.' Option (b) is the correct explanation. Option (a) and (c) are incorrect literal advice about books. Option (d) is the exact assumption the proverb warns against.

**Rule: Understanding Idiomatic Expressions.** The idiom 'call it a day' means to decide to stop doing something, especially working, for the rest of the day. The context of having worked for 'ten hours straight' and postponing the rest of the work makes the meaning clear. Option (b) is the correct definition. Option (a) is a literal misinterpretation. Options (c) and (d) are unrelated actions.

**Rule: Understanding Idiomatic Expressions.** A 'cock and bull story' is an improbable, elaborate, and false story or excuse. The subject of being 'abducted by aliens' is a classic example of something unbelievable. Option (c) is the correct definition. Option (a) is a literal interpretation. Option (b) is the opposite. Option (d) describes the length, not the credibility, of a story.

**Rule: Understanding Idiomatic Expressions.** The idiom 'hit the sack' (or 'hit the hay') is a colloquial expression that means to go to bed or go to sleep. The context of a 'long day of hiking' suggests tiredness and the need for rest. Option (c) is the correct meaning. Option (a) is a literal interpretation of 'hit the sack.' Options (b) and (d) are unrelated actions.

**Rule: Understanding Idiomatic Expressions.** The idiom 'the elephant in the room' refers to a significant and obvious problem or topic that everyone is aware of but avoids discussing. The phrase 'nobody wants to discuss' is a direct clue. Option (b) correctly defines this idiom. Option (a) is a literal and alarming misinterpretation. Option (c) is the opposite. Option (d) is a possible but incorrect literal interpretation.

**Rule: Understanding Idiomatic Expressions.** The idiom 'stick to one's guns' means to maintain one's position or opinion, especially in the face of opposition. The context 'even when everyone else disagrees' perfectly illustrates this meaning. Option (b) is the correct definition. Options (a), (c), and (d) are all incorrect, literal interpretations of the word 'guns'.

**Rule: Understanding Idiomatic Expressions.** The idiom 'smoke and mirrors' refers to trickery or deception, something that is designed to mislead people into believing it is more impressive or substantial than it really is. 'Empty promises' are a form of deception. Option (c) is the correct definition. Option (a) is the literal origin of the phrase, from stage magic. Option (b) is the opposite. Option (d) is an unrelated interpretation.

**Rule: Understanding Idiomatic Expressions.** The proverb 'you can't have your cake and eat it too' means that you cannot have or do two good things at the same time that are contradictory. The example of saving money versus spending it illustrates this choice between two mutually exclusive options. Option (b) correctly explains the proverb's meaning. Options (a), (c), and (d) are all literal or incorrect interpretations related to cake.

**Rule: Understanding Idiomatic Expressions.** The idiom 'bite the bullet' means to face a difficult or unpleasant situation with courage and determination. Confessing to breaking a window is a difficult act that requires courage. Option (c) correctly defines this idiom. Option (a) is the literal action from which the idiom originates (soldiers would bite bullets during surgery without anesthesia). Option (b) and (d) are the opposite of taking responsibility.

**Rule: Understanding Idiomatic Expressions.** The idiom 'know the ropes' means to be familiar with all the details and procedures of a particular task or situation. A 'seasoned sailor' would certainly be an expert in navigation. Option (b) is the correct definition. Option (a) and (c) are literal interpretations of 'ropes.' Option (d) is an incorrect assumption.