The word Diligent describes someone who has or shows care and conscientiousness in one's work or duties. It implies persistent and careful effort. Therefore, the most fitting synonym among the options is Hardworking (option B).
A diligent person applies themselves with great effort and attention to detail, ensuring tasks are completed thoroughly and carefully. For example, a “diligent student” studies consistently, and a “diligent researcher” conducts thorough investigations. Option A, “Lazy,” is an antonym, describing an unwillingness to work or exert effort. Option C, “Weak,” describes a lack of physical or mental strength, which is unrelated to diligence. Option D, “Slow,” describes pace, which is not necessarily the defining characteristic of diligence, as one can be slow but still diligent. Understanding “diligent” helps to commend individuals who demonstrate dedication, thoroughness, and sustained effort in their responsibilities, highlighting their commitment to quality work.