Writing and Reading

      [1] Butterflies, for example, find nectar-filled flowers by smell, while mosquitoes are pros at sniffing out people or other potential sources of the blood meals they require. [2] The success of insects—the most diverse group of multicellular organisms on Earth—is linked to their ability to detect and distinguish an enormous variety of volatile chemicals in the environment, allowing them to thrive in a wide range of ecological niches. [3] While humans rely strongly on sight and hearing to navigate their environment, for insects it’s all about odor. [4] Butterwick’s research reveals how the shape of a key insect “sniffer” molecule makes this olfactory virtuosity possible. [5] To cope with an almost unlimited range of chemical odorants in the environment, insects have evolved a similarly enormous variety of odor receptors. [6] Researchers estimate there are tens of millions of distinct receptors, each capable of detecting a different chemical.

To make the paragraph most logical, sentence 3 should be placed