Correct option is D. An unexpected result occurs during the initial phase of a study; the study is modified in response to this result and the results are interpreted and evaluated.
The writer begins this passage by stating that the ability of birds to fly has long been a source of debate among scientists.
The article then goes on to explain that when a group of students challenged Ken Dial to come up with new data on this hotly debated topic, he devised an experiment to study the evolution of flight by observing how baby Chukars learn to fly. Dial noted the unusual way the little Chukar "used its wings and legs cooperatively" to climb over hay bales during the experiment. Following that, he devised a series of experiments to investigate his discovery.
<h3>Below is the passage mentioned in the question is from Thor Hanson, Feathers by Thor Hanson - </h3>
" At field sites around the world, Ken Dial saw a
pattern in how young pheasants, quail, tinamous,
and other ground birds ran along behind their
parents. “They jumped up like popcorn,” he said,
5 describing how they would flap their half-formed
wings and take short hops into the air. So when a
group of graduate students challenged him
to come up with new data on the age-old
ground-up-tree-down debate, he designed a project
10 to see what clues might lie in how baby game birds
learned to fly.
.............................................................
Ken called the technique WAIR, for wing-assisted
incline running, and went on to document it in a
wide range of species. It not only allowed young
birds to climb vertical surfaces within the first few
weeks of life but also gave adults an energy-efficient
65 alternative to flying. In the Chukar experiments,
adults regularly used WAIR to ascend ramps steeper
than 90 degrees, essentially running up the wall and
onto the ceiling.
In an evolutionary context, WAIR takes on
70 surprising explanatory powers. With one fell swoop,
the Dials came up with a viable origin for the
flapping flight stroke of birds (something gliding
animals don’t do and thus a shortcoming of the
tree-down theory) and an aerodynamic function for
75 half-formed wings (one of the main drawbacks to the
ground-up hypothesis). "
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