The correct answer is D: Higher gain. Most two-element Yagis with normal spacing have a reflector instead of a director because a reflector provides higher gain than a director in a two-element configuration. A reflector creates more forward gain than a director would. In a two-element Yagi, a reflector (element behind the driven element, longer than resonance) provides more forward gain than a director (element in front, shorter than resonance). The reflector creates a better forward/backward ratio and concentrates more power in the forward direction. While a director also provides gain, a reflector is more effective in a simple two-element design. This is why most two-element Yagis use a reflector - it gives the best gain for the simplest configuration. Multi-element Yagis use both reflectors and directors, but two-element designs typically use a reflector.