Final answer:
The function Y = 1/2 X - 3 is a linear function with its graph being a straight line that slopes upward to the right with a y-intercept of -3, which corresponds to answer option D.
Step-by-step explanation:
The function Y = 1/2 X - 3 is a linear function whose graph is a straight line. This can be deduced from the form of the equation, which matches the general linear equation form y = a + bx, where b represents the slope and a represents the y-intercept. In this case, b is 1/2, which indicates that the slope is positive, causing the line to slope upward to the right. The y-intercept (where the line crosses the y-axis) is -3, suggesting that the line crosses the y-axis at a negative value. Given these characteristics, the correct answer to the question is option D: It is a linear function, and its graph is a straight line.