**Rule: Understanding Idiomatic Expressions.** The idiom 'a bitter pill to swallow' refers to a difficult or unpleasant piece of information that one is forced to accept. A tax increase is often seen as an unwelcome necessity. Option (c) is the correct definition. Option (a) is the literal concept from which the idiom is derived. Option (b) is the opposite. Option (d) is incorrect.

**Rule: Understanding Idiomatic Expressions.** The idiom 'an old hand' refers to a person who is very experienced and skilled in a particular activity. Knowing 'all the tricks to win' is a sign of extensive experience. Option (c) is the correct definition. Option (a) is a literal interpretation. Option (b) is the opposite. Option (d) might be true of the person, but it is not the meaning of the idiom itself.

**Rule: Understanding Idiomatic Expressions.** The idiom 'a flash in the pan' refers to something that has a sudden and brilliant but brief and temporary success. The description of being successful 'for a few months' and then 'quickly failed' perfectly matches this definition. Option (b) is the correct meaning. Option (a) and (c) are literal misinterpretations. Option (d) is the opposite.

**Rule: Understanding Idiomatic Expressions.** The idiom 'have a bone to pick with someone' means that you have a reason to be annoyed with them and you want to talk to them about it. The 'mess you left in the kitchen' is the source of the grievance. Option (b) correctly defines this situation. Options (a) and (c) are incorrect literal interpretations. Option (d) is the opposite of a complaint.

**Rule: Understanding Idiomatic Expressions.** The idiom 'sitting on the fence' means to remain neutral or undecided in a dispute or contest. The fact that he 'hasn't decided which candidate to vote for' is a clear example of this indecision. Option (a) is the correct definition. Option (b) and (c) are literal interpretations. Option (d) is the opposite of being undecided.

**Rule: Understanding Idiomatic Expressions.** The idiom 'at each other's throats' means to be arguing or fighting fiercely. While it can imply physical violence, in the context of a political debate, it refers to intense verbal conflict. Option (c) is the most appropriate meaning. Option (a) is a possible but too literal interpretation. Option (b) is nonsensical. Option (d) is the opposite.

**Rule: Understanding Idiomatic Expressions.** The idiom 'play it by ear' means to improvise or make decisions as you go along, depending on the situation. The uncertainty about the number of guests makes advance planning difficult, necessitating improvisation. Option (b) is the correct definition. Option (a) and (c) are incorrect literal interpretations. Option (d) is the opposite of what the idiom means.

**Rule: Understanding Idiomatic Expressions.** The idiom 'a feather in one's cap' refers to a notable achievement or a source of pride. A 'promotion' is a significant professional accomplishment. Option (c) correctly defines this idiom. Option (a) is a literal interpretation. Option (b) is the opposite of a proud achievement. Option (d) is an incorrect interpretation based on the literal quality of a feather.

**Rule: Understanding Idiomatic Expressions.** The idiom 'throw in the towel' means to quit or surrender. It originates from boxing, where a fighter's corner would throw a towel into the ring to signal defeat. The encouragement to keep going because he is 'so close to finishing' makes the meaning clear. Option (a) is the correct definition. Options (b) and (c) are literal interpretations. Option (d) is an unrelated action.

**Rule: Understanding Idiomatic Expressions.** The full idiom is 'a jack of all trades is a master of none.' It refers to a person who has a competent range of skills in various areas but does not have outstanding expertise in any particular one. The phrase itself provides the definition. Option (b) is the correct explanation. Option (a) contradicts the 'master of none' part of the idiom. Options (c) and (d) are incorrect interpretations.