English Grammar: Prepositions and Conjunctions

詳解：The correct preposition after 'good' is 'at' when referring to a skill or subject (e.g., good at mathematics). 'In' is used for areas like 'good in class', but not with specific subjects. 'On' and 'with' are not used with 'good' in this context. Students often confuse 'at' and 'in' because both can indicate competence, but 'at' is the standard choice for skills.

詳解：'Until' indicates a time up to which an action continues, fitting the meaning of waiting for completion. 'Because' shows cause, 'although' shows contrast, and 'unless' means 'if not'. Students might pick 'unless' thinking it means 'until', but 'unless' implies a condition, not a time frame.

詳解：We use 'at' for specific times (3 p.m.) and 'on' for days (Monday). 'In' is used for months, years, etc., not for specific times or days. Students often mix up 'in' and 'on' for days, but 'on' is correct for days and dates. Option C incorrectly places 'on' for time and 'at' for day.

詳解：'But' shows contrast between being tired and continuing to work. 'So' indicates a result, which would mean he continued because of tiredness, which is illogical. 'Or' offers an alternative, and 'because' gives a reason, but the second clause is not a reason for being tired. Students often use 'so' incorrectly for contrast.

詳解：The adjective 'interested' is followed by the preposition 'in' (interested in + gerund). 'On', 'at', and 'for' are not used with 'interested' in this context. Students might choose 'for' thinking it expresses purpose, but 'interested in' is a fixed expression.

詳解：'Or' is used to indicate a consequence or alternative: if you don't study hard, you will fail. 'And' would imply both actions, 'but' shows contrast, and 'so' shows result, but the first clause is a condition for the second, and 'or' is the correct connector for a warning. Students often confuse 'or' and 'so', but 'so' would make the second sentence a result of studying hard, which is not intended.

詳解：'Under' is the most common preposition for directly below something, and it is the best choice for a cat hiding under a bed. 'Below' is often used for a lower level or position, not necessarily directly under. 'Beneath' is more formal and less common in everyday speech. 'Across' means from one side to the other. Students might pick 'below' but 'under' is more natural and idiomatic.

詳解：'Because' introduces a reason: she was sick, so she didn't come. 'Although' would show contrast, which doesn't fit. 'Unless' means 'if not', and 'until' refers to time. Students might choose 'although' thinking it shows a cause-effect relationship, but 'although' introduces a concession, not a reason.

詳解：We use 'by' to indicate the means of transport (by bus, by car, by train). 'On' is used for specific vehicles like 'on the bus' when referring to being inside, but the phrase 'go to school by bus' is the standard expression. 'In' is used for cars but not buses in this context, and 'with' is incorrect. Students often confuse 'by' and 'on'.

詳解：'But' is used to show contrast between liking tea and not liking coffee. 'And' would suggest both are true without contrast, which is possible but less precise. 'So' implies a result, which is illogical. 'Or' offers a choice. The contrast is clear, so 'but' is the best answer. Students often choose 'and' but 'but' more accurately reflects the contrasting ideas.