Over the centuries, various theories have been （） to explain the origin of alphabetic writing.

单项选择题The physical shape and coloring of many animals are the result of gradual （） to particular circumstances.

A．modification
B．variation
C．application
D．adaptation

单项选择题One study found that job applicants who make more eye contact are （） as more alert, dependable, confident and responsible.

A．referred
B．perceived
C．recommended
D．presumed