Read this excerpt from 'the city without us" by alan weisman:
many foreign ornamentals - double roses, for example - will
wither with the civilization that introduced them, because they
are sterile hybrids that must propagate through cuttings. when
the gardeners that clone them go, so do they. other pampered
colonials like english ivy, left to fend for themselves, lose to their
rough american cousins, virginia creeper and poison ivy.

which sentence best states the main idea of this section of the chapter?

a. double roses require people to clone them in order to survive.

b. nature would quickly take over if humans were to disappear.

c. some types of flowers can survive only if humans tend to them

d. virginia creeper and poison ivy survive better than english ivy.