figure 1 has a positive slope

figure 2 has a negative slope

figure 4 has a slope for zero

figure 3 has an undefined slope

hope it helps

1. That is a difficult question. I would say the slope is positive but I may be wrong
2. The one with the slope being negative.
3. The one with zero slope

4. I'm not sure exactly, but it's like a circle with no edges or anything.