According to Naomi Nakayama of the University of Edinburgh, the reason seeds from a dying dandelion appear to ﬂoat in the
air while ______ is that their porous plumes enhance drag, allowing the seeds to stay airborne long enough for the wind to
disperse them throughout the surrounding area.
falling,
falling:
falling;
falling
Choice D is the best answer. The word “falling” occurs in the middle of a clause and isn’t part of a supplement, so we don’t
need any punctuation after it. We can see this more clearly if we simplify the rest of the sentence: “The reason seeds appear
to ﬂoat while falling is that their plumes enhance drag.” .
Choice A is incorrect. This doesn’t complete the text in a way that conforms to the conventions of Standard English. The
word “falling” occurs in the middle of a clause and isn’t part of a supplement, so we don’t need any punctuation after it. We
can see this more clearly if we simplify the sentence: “The reason seeds appear to ﬂoat while falling is that their plumes
enhance drag.” . Choice B is incorrect. This doesn’t complete the text in a way that conforms to the conventions of Standard
English. The word “falling” occurs in the middle of a clause and isn’t part of a supplement, so we don’t need any punctuation
after it. We can see this more clearly if we simplify the sentence: “The reason seeds appear to ﬂoat while falling is that their
plumes enhance drag.” . Choice C is incorrect. This doesn’t complete the text in a way that conforms to the conventions of
Standard English. The word “falling” occurs in the middle of a clause and isn’t part of a supplement, so we don’t need any
punctuation after it. We can see this more clearly if we simplify the sentence: “The reason seeds appear to ﬂoat while falling
is that their plumes enhance drag.” .