Which of the Following Systems Use(s) the Heliostats to Focus

Multiple Choice

Which of the following systems use(s) the heliostats to focus the Sun's energy on molten salt water for creating steam?
I. Solar power tower
II. Parabolic trough
III. Dish/engine

A) I only
B) II only
C) I, II, and III
D) I and II
E) I and III