Doctor : patient : : A. politician : constituent B. constitution : preamble C. podiatrist : hand D. aggressor : rival E. genuflect : substitute

A. politician : constituent

A doctor is to a patient as a politician is to a constituent.

A doctor is the professional expert treating (involved with) the amateur.

A politician is a person who is professionally and knowledgeably involved in politics. A constituent is a voting member in a political election; it is higher than a regular person, but under a politician.

Thus, a politician is the professional expert involved with the amateur.