The answer is choice D) Angle F
Why is this not proper notation? Because there are two possible angles with point F as the vertex. If we only had triangle DFG to worry about, then we can say "angle F" without mentioning other points, and we'd know exactly what angle is being referenced. In this case, angle F could refer to either angle DFG or angle DFE. Note how F is the middle letter in each case.
