Consider the Following Model of the IS Curve Without an International

Consider the following model of the IS curve without an international sector:
Consumption: $C _ { t} / \bar { Y } _ { t } = \bar { a } _ { c } - \bar { b } _ { c } \left( R _ { t } - \bar { r } \right)$ ; Investment: $I _ { t } / \bar { Y } _ { t } = \bar { a } _ { i } - \bar { b } _ { i } \left( R _ { t } - \bar { r } \right) ;$ Government expenditure: $G _ { t } = \bar { a } _ { g } \bar { y } _ { t }.$ With this formulation, the IS curve is:

A) horizontal
B) vertical
C) less steeply sloped than the "standard" IS curve
D) more steeply sloped than the "standard" IS curve
E) Not enough information is given.