Which of the following describes how biodiversity contributes to the sustainability of a natural environment?

a.
non-native alligator weed forms dense mats that crowd native species in california.

b.
grasslands in the california floristic province have been converted into housing projects, shopping centers, and roads.

c.
acacia trees of central and south america provide shelter for stinging ants, while the stinging ants remove fungal spores from the trees.

d.
european common pine-shoot beetles feed on the shoots of pine trees in the northeastern united states, causing a decrease in the trees' heights and growth.