Green invaders are taking over America. Not invaders from space, but plants! You might not think of plants as dangerous, but in this case they are threatening nature's delicate food chain. The invaders are plants brought here from other countries to make gardens and yards look pretty. Ever since people started to arrive on America's shores, they have carried along trees, flowers, and vegetables from other places. Now there are so many of those plants, they are crowding out the native plants that have lived here since before human settlers arrived. And that's a problem, says Dr. Doug Tallamy. He's insect expert at the University of Delaware. He explains that almost all the plant-eating insects in the United States are specialized, which means they eat only certain plants. Monarch butterfly caterpillars ,for example, dine on milkweed. If people cut down milkweed and replace it with another plant, the butterflies will not have the food source that they need to survive. But the trouble doesn't stop there. When insects can't get the right plants to eat and they die off, then the birds don't have enough bugs for their meals. Tallamy points out that almost all migrating birds depend on insets to feed their young. "We cannot let the plants and animals around us disappear." says Tallamy, "The way to preserve them is to give them food to eat. But when we plant non-native plants, we are _ the food chain, because then we don't have the insects the birds need to live." Fewer of the right plants mean fewer bugs, and fewer bugs mean fewer birds. And that's bad for the Earth, because we need a variety of living things to keep the planet healthy and beautiful. The good news is, garden centers sell native plants. "Just Google 'native plants' and your location, and you can find out which plants really belong where you live," says Tallamy We can know whether a plant is native by   _  .
Googling on the Internet asking Dr. Doug Tallamy looking up in books searching in garden
Question: Green invaders are taking over America. Not invaders from space, but plants! You might not think of plants as dangerous, but in this case they are threatening nature's delicate food chain. The invaders are plants brought here from other countries to make gardens and yards look pretty. Ever since people started to arrive on America's shores, they have carried along trees, flowers, and vegetables from other places. Now there are so many of those plants, they are crowding out the native plants that have lived here since before human settlers arrived. And that's a problem, says Dr. Doug Tallamy. He's insect expert at the University of Delaware. He explains that almost all the plant-eating insects in the United States are specialized, which means they eat only certain plants. Monarch butterfly caterpillars ,for example, dine on milkweed. If people cut down milkweed and replace it with another plant, the butterflies will not have the food source that they need to survive. But the trouble doesn't stop there. When insects can't get the right plants to eat and they die off, then the birds don't have enough bugs for their meals. Tallamy points out that almost all migrating birds depend on insets to feed their young. "We cannot let the plants and animals around us disappear." says Tallamy, "The way to preserve them is to give them food to eat. But when we plant non-native plants, we are _ the food chain, because then we don't have the insects the birds need to live." Fewer of the right plants mean fewer bugs, and fewer bugs mean fewer birds. And that's bad for the Earth, because we need a variety of living things to keep the planet healthy and beautiful. The good news is, garden centers sell native plants. "Just Google 'native plants' and your location, and you can find out which plants really belong where you live," says Tallamy We can know whether a plant is native by   _  .
A. Googling on the Internet
B. asking Dr. Doug Tallamy
C. looking up in books
D. searching in garden
Answer: