Every profession requires you to work both individually and as a member of a team. Different situations require different ways of working. You probably have a preference for one or the other of these. When you answer this question, begin by recognizing that you need to be able to do both of these, and then state your preference, providing the interviewer with a rationale for your choice.
"I function well while working both as an individual contributor and as a member of a highly functional team. There are benefits to both of these work styles. If the problem is simple, requires only my expertise, and can be done relatively quickly, working alone is the best method. However, for complex situations, which require input from many different perspectives and resources provided by individuals with different talents, teaming works best. Given a choice, I would rather work in a team. Not only is this more enjoyable, but it also provides me the opportunity to learn from others."