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.
A．They acquired this ability through recent evolutionary changes.
B．They are not necessarily more intelligent than other animals.
C．Their brains all have an identical structure that governs this ability.
D．They may be able to understand other animal's perspective.
A．Many of her books are bestsellers.
B．She is a shrewd bookstore owner.
C．She is promoting her book in person.
D．She is a salesperson at the bookstore.