Researchers studying parental care in 20 female robins found that every female robin would place a recently collected worm into the first open mouth she saw in her nest. it appeared that the sight of an open mouth triggered the female bird's feeding behavior. to test this hypothesis, a robotic baby robin was added to every one of the 20 nests. the robot baby always had its mouth open, and the female robin always fed it first. we can conclude that

Waste water from industries and domestic sources can be treated by chlorination or ultraviolet radiation. there are pros and cons to using either chlorine or uv radiation to kill harmful microorganisms. what is one reason chlorination would be preferred over ultraviolet radiation? a) chlorine only eliminates visible impurities and is ineffective against microorganisms. b) chlorine not only kills bacteria but provides a residual effect on returning microorganisms. c) uv radiation can be used only to treat drinking water and is ineffective in treating waste water. d) ultraviolet radiation is more effective