________ the lip of an open-pit copper mine, the huge tractors and cranes below look like toys, and people look like tiny ants scurrying about.

Double stars orbit ________.

The bird's egg is such an efficient structure for protecting the embryo inside ________ difficult for the hatchling to break.

Besides rain, ________ is seldom pure.

A dolphin ________ a porpoise in that it has a longer nose.

A symbol of the ancient competition, the Olympic flame burns ________ throughout the games.

Although they are both grown in the United States and exported abroad, corn is not native to America and winter wheat ________.

Although blood ________ a residue in urine and stool samples, it cannot always be detected without the aid of a microscope.

Prospectors rushed to Nevada in 1859 ________ was discovered there.

________ the Christmas shopping season begins.