Determine the correct orientation of change vectors for points along the nullclines.
1) Vertical on blue (T-nullcline), vertical on red (S-nullcline)
2) Vertical on blue (T-nullcline), horizontal on red (S-nullcline)
3) Horizontal on blue (T-nullcline), vertical on red (S-nullcline)
4) Horizontal on blue (T-nullcline), horizontal on red (S-nullcline)