Read the following passage and mark the letter A. B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35 Nanotechnology is the creation and use of materials or devices at extremely small scales. These materials or devices fall in the range of 1 to 100 nanometers (nm). One nm is equal to one-billionth of a meter (.000000001 m), which is about 50,000 times smaller than the diameter of a human hair. Scientists refer to the dimensional range of 1 ...

Read the following passage and mark the letter A. B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35

Nanotechnology is the creation and use of materials or devices at extremely small scales. These materials or devices fall in the range of 1 to 100 nanometers (nm). One nm is equal to one-billionth of a meter (.000000001 m), which is about 50,000 times smaller than the diameter of a human hair. Scientists refer to the dimensional range of 1 to 100 nm as the nanoscale, and materials at this scale are called nanocrystals or nanomaterials.

The nanoscale is unique because nothing solid can be made any smaller. It is also unique because many of the mechanisms of the biological and physical world operate on length scales from 0.1 to 100 nm. At these dimensions materials exhibit different physical properties; thus scientists expect that many novel effects at the nanoscale will be discovered and used for breakthrough technologies.

A number of important breakthroughs have already occurred in nanotechnology. These developments are found in products used throughout the world. Some examples are catalytic converters in automobiles that help remove air pollutants, devices in computers that read from and write to the hard disk, certain sunscreens and cosmetics that transparently block harmful radiation from the Sun, and special coatings for sports clothes and gear that help improve the gear and possibly enhance the athlete’s performance. Still, many scientists, engineers, and technologists believe they have only scratched the surface of nanotechnology’s potential.

Nanotechnology is in its infancy, and no one can predict with accuracy what will result from the full flowering of the field over the next several decades. Many scientists believe it can be said with confidence, however, that nanotechnology will have a major impact on medicine and health care; energy production and conservation; environmental cleanup and protection; electronics, computers, and sensors; and world security and defense.

(Adapted from: Encarta DVD 2009)

The word “that” in paragraph 3 refers to ________