The following diagram shows the unit circle with the arc π/3 drawn:
The secant of an angle in a right triangle is defined as the quotient between the hypotenuse and the side adjacent to that angle in the right triangle.
In this case, the hypotenuse of the right triangle to which the angle of π/3 belongs has a measure of 1, while the side adjacent to that angle has a measure of 1/2. Then, the secant of π/3 is:
Therefore, the correct choice is option D) 2.