"I don't think Prof. Smith meant to be funny this morning, do you"
"No, although I couldn't help _______ at some of his remarks."

A．The invention of agricultural implements and machinery.
B．The development of a system of names for plants.
C．The discovery of grasses that could be harvested and replanted.
D．The changing diets of early humans.

A．To make the passage more poetic.
B．To cite example of plants that are attractive.
C．To give botanical examples that all readers will recognize.
D．To illustrate the diversity of botanical life.