Read the following article and select the best answer. Article: In spring, you may have seen white foam on a green tree or other plants. As a matter of fact, the foam is where young spittlebugs live. These insects are protected by the foam, and they usually don't do much harm to the plants. As we all know, in late summer, a mother spittlebug lays her eggs on the plant. The babies will hatch in spring. After they come to the new world, they begin to eat juice from the plant. The babies eat more juice than their bodies need for food. The extra juice mixes with a special waste that the spittlebugs produce. When this fluid is released, it mixes with the air, forming bubbly foam. What is so great about having a foam home? The space inside is so wet that it can keep the bugs' soft bodies from drying out. And the foam tastes bad, so it keeps away most animals that would eat the bugs. Some birds will reach their heads through the foam to find the bugs. Wasps and ants might eat them, too. But most of the bugs stay safe inside the foam. Once the bugs have grown into adults, they stop making foam. They leave their homes and jump from plant to plant in search of food. The adults look a little like tiny frogs. For this reason they are also called froghoppers. If you see some foam on a plant, you might want to take a careful look inside. Gently push some of the foam aside with a small stick. Deep inside you may see a few insects eating plant juice. They might also be making more foam. Be sure to push the foam back after a moment to cover the insects and keep them safe. Soon the spittlebugs will grow up and leave their foam home. They will join the other insects in the grassland. Question: According to the passage, the white foam _ . - does much harm to the plant - protects the plant from being harmed - is where a mother spittlebug is living - is plant juice mixed with spittlebugs' waste and the air
A:
is plant juice mixed with spittlebugs' waste and the air