This isn't a trick question, and the best response isn't necessarily just to say yes, without hesitation. There are innumerable factors that could have a bearing on what you might say, not least the vexed issue of waiting to hear back about other applications. But let's not assume that being honest is always a bad thing. The crucial point is that, before you get in the room, you should take time to think through whether you would accept the job, and to discuss it with peers and mentors.