A slope field is observed to have the following features:
• The slope is zero along both coordinate axes.
• In Quadrants I and III the segments tilt upward to the right.
• In Quadrants II and IV the segments tilt downward to the right.
Which differential equation could produce this slope field?
a) dxdy=x+y
b) dxdy=x2y2
c) dxdy=xy
d) dxdy=xy