Correct Answer:
B. at
The correct answer is B: at. This question tests your knowledge of common prepositions used with adjectives to form idiomatic expressions.
The phrase 'good at' is a standard idiom in English used to express proficiency, skill, or talent in a particular subject, activity, or area. When you say someone is 'good at mathematics,' it means they possess a strong ability or skill in that subject.
- A: in is generally used to indicate location or inclusion (e.g., 'She is in the room' or 'She is interested in science'). While one might say 'She is good in class,' it doesn't specifically convey skill in a subject as effectively as 'good at'.
- C: on is typically used to indicate position on a surface, a topic of discussion, or a schedule (e.g., 'The book is on the table,' 'They are working on a project,' or 'The meeting is on Tuesday.'). It does not fit the context of expressing skill.
- D: for is used to indicate purpose, benefit, or duration (e.g., 'This is good for your health,' 'She studied for two hours,' or 'This gift is for you.'). It does not convey proficiency in a subject.
Thus, 'good at' is the only grammatically correct and idiomatic choice to express skill in mathematics.