The least square regression results of a model are known as follows:

Where, Y: government bond price ($100), X: interest rate (%).

_i=101.4-4.78X，t (45.2) ( 1.53) ，n=30 ，R²=0.31

(1) Is the sign of the coefficient correct, and give the reason.

(2) Why is the left side Y instead of Y.

(3) Whether the error term u is omitted in this model; (4) What is the economic significance of the model parameters?