Item 8 Read the passage.

Colony Collapse Disorder

In 2006, beekeepers throughout the United States began to notice something new—and troubling. Adult honeybees, known as worker bees, were disappearing from their hives, seemingly abandoning them. Few or no dead bees were found in the hives, while the queen and larvae were alive and well but without the swarm of worker bees that typically attended them to keep them alive. What had happened?

The phenomenon became so widespread that it soon received a name, Colony Collapse Disorder (CCD) . There was no denying that CCD was a problem; after all, American agriculture depends on the work of honeybees and other pollinators. At least three-quarters of the crops grown in the United States depend on honeybee pollination for their survival. These include such staples as strawberries, blueberries, apples, broccoli, asparagus, and almonds. Without them, both farmers and anyone who enjoys fresh fruits and vegetables will suffer.

But what is causing this problem? Scientists have rigorously studied a variety of possible causes, ranging from genetically modified crops to climate change to cell phone towers. Sadly, nothing has shown to be the cause of the problem. The most likely culprits are pathogens, or disease-causing organisms. These have been found in larger numbers in colonies affected by CCD than in those unaffected. But these pathogens have included various viruses and bacteria, some found in greater concentrations in different parts of the country. If CCD is caused by a single disease, identifying that disease will be difficult.

The CCD epidemic is most likely the result of multiple causes—pathogens, poor nutrition, pesticides, lack of genetic diversity, and habitat loss. Efforts to prevent colony loss have been mildly successful. The number lost has declined each year since 2008. But until a solution to this problem is found, CCD will remain a concern that will threaten not only the future of bees, but also of the people who rely on the food that they help produce.

Read the sentence from “Colony Collapse Disorder.”

Scientists rigorously studied a variety of possible causes, ranging from genetically modified crops to climate change to cell phone towers.

How does the use of the word rigorously affect the tone of the excerpt?

It creates a determined tone.

It creates a self-assured tone.

It creates a confident tone.

It creates an excited tone.