Question

wind tunnels: a test of form and function
look up at the sky, and you are likely to see airplanes, helicopters, and other types of aircraft soaring high above you. what you might not realize is that these aircraft all had to pass a series of tests to be considered safe enough to fly. one tool that researchers use when testing aircraft is a wind tunnel. this essential machine helps scientists improve the design of aircraft
how wind tunnels work
wind tunnels are tubes that vary in size depending upon the object being tested. airplanes require huge wind tunnels. at one end of the tunnel is a fan blowing air. the fan can be set to different speeds and directions. an object is held in place in the tube, either with physical restraints or with the use of magnets. then the fan blows air around the object, creating an effect similar to flying.
wind - tunnel experiments help us understand how an object reacts to different wind situations. the tests can show how wind speed and direction affect the object while taking off, flying, and landing. researchers search for hidden flaws in the design of objects such as an aircraft. to help do this, they often add smoke or colored dye to the air. then the researchers photograph how the smoke or dye moves over the object while the fans are on
how does the author provide evidence to support the argument that having many different wind tunnels is necessary?
a by listing the various sizes of objects that are tested in wind tunnels
b by describing how varying fan speeds can create a cycle of air
c by identifying different types of spacecraft that benefit from wind tunnel tests
d by explaining that improving spacecraft design is a continual goal

Explanation:

The passage mentions that wind - tunnels vary in size depending on the object being tested. Different sized objects (like different aircraft) require different sized wind - tunnels, which supports the need for many different wind - tunnels. Option b focuses on fan speed, option c on types of spacecraft (while the passage is more about aircraft in general), and option d on the goal of improving spacecraft design rather than the need for different wind - tunnels.

Answer:

A. by listing the various sizes of objects that are tested in wind tunnels