4. The state representation of a second-order system is x_1 ¼ x1 þ u; x_2 ¼ x1 2×2 þ u. Consider the following statements regarding the above system: 1. The system is completely state controllable. 2. If x1 is the output, then the system is completely output controllable. 3. If x2 is the output, then the system is completely output controllable. (a) 1, 2 and 3 are correct (b) 1 and 2 are correct (c) 2 and 3 are correct (d) 1 and 3 are correct