Answer: A. Routines.
Explanation: A transitive verb is one that is used with an object (something or someone that receives the action of the verb), transitive verbs are usually action verb (like write, eat, want, drink, etc.). In the given sentence "Many skaters practice their routines in cold ice rinks before dawn" the transitive verb is "practice" and its object is "routines", we can know this by asking a "what" question to the verb, in this case "what many skaters practice?"