Answer is highlighted on the attachment
Reason
Number of people and amount of trash = more people equals more trash so the slope will go up.
Distance to your destination and time = further distance traveled will show an increase in time so an upward slope.
Number of squirrels and number of acorns hidden. The more squirrels there are, the more acorns will be hidden showing an upward slope.
The other two have no relationship to each other.