【单选题】

Have you ever heard of a flower whose seeds are carried and spread by elephants The rafflesia, a rare blossom, is very unusual. Found in the rain forests of Sumatra, the rafflesia is the world’s largest flower, measuring three feet in diameter!

This giant flower is a parasite—it needs another plant to live on. It lacks the structures needed to survive alone. The rafflesia has no stem or leaves. It is all flower. It attaches itself to the roots of other plants and sucks their juices. The flower’s favorite home is the root of the vine, which grows above grounD、
The rafflesia seems to burst right out of the forest floor. Its blossom weighs fifteen pounds! It has thick, spotted petals that give off a rotten smell. The center is about the size of a household bucket.After a rain, it may hold up to twelve pints of water!
After the rafflesia dies, it becomes a pool of thick liquid in which its seeds float.Elephants wandering through the forest step into the mushy pool, and the seeds glue themselves to their feet.As the animals stomp through the forest, their sticky feet pick up twigs and leaves. The elephants try to rid themselves of the sticky mess, in the same way people try to get bubble gum off their shoes. The elephants rub their feet against the roots of the vine. In no time, seeds left on the vine grow into more monstrous flowers!
As used in this passage, "structures" means ______.
A、enduranceB、organization
C、necessary partsD、energy