Question

1. calculations show that we have already passed the planetary boundaries for three systems. these include: a. climate change b. nitrogen cycling c. ocean acidification d. a and d e. all of the above

Explanation:

Planetary boundaries for climate change, nitrogen cycling (a biogeochemical cycle), and ocean acidification (related to climate and marine chemistry) are all systems where calculations show we've crossed boundaries. So "all of the above" (E) is correct.

Answer:

E. all of the above