Firstly light is an external stimuli. in plants - shoots are positively phototrophic while roots are negatively phototrophic.
I just had this answer but it hasn't been graded. I put 1. Meteor impacts, 2. volcanic gases and 5. Milankovitch cycles. I didn't put earthquakes because I wouldn't think it would affect the climate changing since they just affect ground movement.
Answer:
B. Bacteria are introduced to break down hydrocarbons in an oil spill.
