Directions:
Read the passage about radar and complete the statement.





Radar is a system that measures the position and movement of objects from a distance. Radar systems use radio waves. Something as solid as an airplane or automobile or something as insubstantial as a cloud can be observed using radar. ____?____ substances can be measured.


The radar system is composed of a transmitter and receiver. The transmitter sends out pulses of radio waves. These pulses bounce back when they hit an object. The receiver measures these reflected pulses. These reflections show the position and motion of the object. Usually the transmitter rotates or scans back and forth to find all objects in a certain area. By using radio waves instead of visible light, objects can be detected at great distances. A radar device can be small enough to be held by hand, or it can be a giant radar antenna used to track objects in space.


Many different people use radar. Police use it to find speeding drivers. Airports use it to control where planes fly. Most commercial airplanes have their own radar on board that warns of possible collisions with nearby aircraft. Radar can be used to track storms. Astronomers use it to study objects in the solar system. Different ________ use radar.


Radar originally stood for “Radio Detection and Ranging.” No one person invented radar. During the early 20th century, different scientists contributed to its development. It was originally designed to detect airplanes and ships for military purposes. Radar was first used for practical purposes in World War II. Both sides raced to improve their radar capabilities. After the war, radar was used for other purposes. In 1946, radar beams were bounced off of the moon. Many people ________ radar technologies.


Stealth technology attempts to make objects invisible to radar. The United States has developed stealth fighter and bomber planes. They use special coatings and shapes to make it harder for radio waves to bounce off of them. They are trying to ________ the reflection of radar waves.


Question

Choose the answer that goes in the ____?____.
Responses

Several
Several

Limited
Limited

Unfamiliar
Unfamiliar

Normal