The correct answer is (a) Positive.
The aggregate consumption curve is a graph that shows the relationship between aggregate consumption and aggregate income. According to simple Keynesian theory, the aggregate consumption curve is upward-sloping, which means that as aggregate income increases, aggregate consumption also increases. This is because as people have more money, they are able to spend more money on goods and services.
Option (b) is incorrect because the aggregate consumption curve is not downward-sloping. Option (c) is incorrect because the aggregate consumption curve is not horizontal. Option (d) is incorrect because the aggregate consumption curve is not vertical.