Yes you can select undecided or undeclared. Actually, undecided is the single most popular major. Statistics show that students change their major by the end of their sophomore year, thus giving them adequate time for course exploration. This is especially true in the fields of engineering, computer science, and biomedicine. According to UC Berkeley, a students can major in any field as an undergraduate, as long as they fulfill the following pre-medical requirements to prepare for medical school.
Some schools require calculus, advanced biology and advanced chemistry.
Select an academic major that interests you and allows you the flexibility to take the required pre-med courses. This is a very popular question, especially among juniors. Colleges tell me that there is no one activity that is better than another. Students should select clubs, volunteer work, etc. One college rep recently said that their admission decision never comes down to the quantity of students activities.