Nancy took a breath and gathered her thoughts. She imagined that passing through the gray-zone door into Level 4 was like a space walk, except that instead of going into outer space, you went into inner space, which was full of the pressure of life trying to get inside your suit. People went into Level 4 areas all the time at the Institute, particularly the civilian animal caretakers. But going into a containment zone to perform a necropsy on an animal that had died of an amplified unknown hot agent was something a little different. This was high-hazard work. –The Hot Zone, Richard Preston What is the central idea of this excerpt from The Hot Zone?
A. animal necropsies are done only by trained professionals.
B. People go into Level 4 areas all the time at the Institute.
C. Entering Level 4 is like going into inner space.
D. Working in a containment zone is very dangerous.

Consider the text from "machu picchu: a city in the sky” and its central idea. informational text: every year, thousands of tourists come to peru to see machu picchu. to reach machu picchu, tourists can hike along the famous inca trail. the trail covers twenty-six miles. it winds through beautiful mountains, forests, and jungle. visitors can also take a bus or train ride up to the ruins. the train takes you past miles of farmland along the urubamba river valley. above are the andes mountains. the tops of the mountains are often covered with mist. then, the train goes up a mountain on a winding road. the road climbs almost 1,640 feet. other incan ruins can be seen beside the road. most are very small compared to the city ahead. central idea: tourists enjoy visiting machu picchu in the mountains of peru. what supporting detail is most important to include in a summary of this text? people can hike the inca trail or take a train or bus to reach machu picchu. when people travel to machu picchu, they see miles of surrounding farms. people are surprised by the mist on the peaks of the andes mountains. when people visit machu picchu, they sometimes see other smaller ruins.