Step 1: Write the equation:
$C = a + bY$, where $a > 0$ is autonomous consumption (consumption even at zero income) and $0 < b < 1$ is the MPC.
Step 2: Read the slope directly:
In any linear equation $y = mx + c$, the coefficient of $x$ is the slope. Here $b$ is that coefficient, and since $b > 0$, the line must rise from left to right.
Step 3: Confirm with two points:
At $Y=0$, $C=a$. At $Y=100$, $C=a+100b > a$. Consumption strictly increases as income increases, confirming an upward slope.
Final Answer:
Option A, upward sloping.