A．All of the far-red light that reaches plants is used to blossom.
B．Plants flower more rapidly in response to far-red light than to red light.
C．Plants absorb more of the red light that reaches them than of the far-red light.
D．Red-light is absorbed more slowly by plants than far-red light is.

A．Throat markings trigger aggressive behavior in other magpies.
B．Throat markings are extremely rare in magpies.
C．Magpies cannot see their throat markings without looking in a mirror.
D．Magpies cannot easily remove a mark from their throats.

A．He is surprised that the studies have not been copied.
B．He believes the study's findings are not very meaningful.
C．He expects that further studies will show similar results.
D．He thinks that it confirms what is known about some birds.