The slope of a line can be in two forms generally.
It can either be rising or falling
When it rises, the slope comes from the left hand side of the graph and moves upwards. The sign of the slope here is positive and this represents an increasing function. What this means is that as the x-value increase, the y-value increases.
In the second case, we can have a falling line. It comes from the left hand side of the grpah and falls towards the positive x-axis. The slope in this case has a negative value and it is a decreasing function. It represents a decreasing relationship between the x and the y values.
Let us have a pictorial representation of both;
Looking at the pictorial representation, we can see that the given graph looks exactly like the shape on the left
This means that the slope is negative and it represents a decreasing function. So our correct answer ticks in this case are negative slope and decreasing function
Meanwhile, for a constant slope, the value of the function is the same regardless of the x-value. It can be shown as follows;