Nhận biết (M1)

A researcher hypothesized that urban songbirds of a certain species sing at a higher pitch than their rural counterparts in order to be heard over the low-frequency rumble of traffic. To investigate, she recorded the songs of many individuals of this species across a range of urban and rural sites.

Which finding, if true, would most directly support the researcher's hypothesis?

• A.

  Urban birds of the species were, on average, slightly smaller than rural birds.

• B.

  The urban recordings contained more background noise overall than the rural recordings.

• C.

  Within urban sites, birds nearer to busy roads sang at higher pitches than those in quieter parks.

• D.

  Rural birds of the species sang more often at dawn than urban birds did.