The signal flow diagram for a certain feedback control system is shown in figure.

Now consider the following set of equations for the nodes

1. $$x2 = a1 \times 1 + a9 \times 3$$
2. $$x3 = a2 \times 2 + a8 \times 4$$
3. $$x4 = a3 \times 3 + a5 \times 2$$
4. $$x5 = a4 \times 4 + a6 \times 2$$

Which of the following are correct?

A

1, 2 and 3

B

1, 3 and 4

C

2, 3 and 4

D

1, 2 and 4