Answer:
21) falls
22) vertical
23) rises
24) rises
25) falls
26) horizontal
27) rises
28) horizontal
29) falls
Step-by-step explanation:
We shall use the slope formula
to calculate the slopes of the line passing through each pair of point.
21: (3,1), (2,6)
The slope is 
.
A negative slope means this line falls
22) (-2,5), (-2,4)
The slope is
= undefined
An undefined slope means this line is vertical
23) The given point is (0,8) (2,10)
The slope is 
A positive slope means this line rises
24) The points are (-3,-3), (3,1)
The slope is 
A positive slope means this line rises
25) The points are: (5,0) (6,-2)
Slope: 
A negative slope means this line falls
26) The points are (-2,-8) , (5,-8).
Slope: 
A zero slope means this line is horizontal
27) The points are: (-1,2) , (5,3)
Slope: 
A positive slope means this line rises
28) The points are:
, (-1,4)
Slope: 
A zero slope means the line is horizontal
29) The points are: 
Slope: 
A negative slope means this line falls.