What should I do if a department interests me but I have not studied one of its preferred science subjects?

First check the latest admissions guidelines and department information to determine whether the subject is required for application or examination, or merely recommended. If it is not required, look into available examination-subject choices, introductory or remedial classes, and ways to build the necessary foundation independently. If it is required, check whether another eligible subject or admissions route is available, and ask the admissions office or department specifically about eligibility for students who have not taken the subject, the knowledge expected after enrollment, and recommended preparation.