The helicopter is able to hover in ___________ powered rotors produce lift even at zero forward speed.

______________provided a living for nearly 90 percent of the population of the American colonies.

Story of a Bad Boy,a semiautobiographical novel by Thomas Bailey Aldrich, ranks high among books ___________ have incorporated their boyhood experiences.

North Carolina's outer banks are a chain of low, narrow islands ___________ the mainland from the frequent Atlantic storms in the area.

__________ range in color from pale yellow to bright orange.

___________ of precious gems is determined by their hardness, color, and brilliance.

_____________a tornado spins in a counterclockwise direction in the northern hemisphere, it spins in the opposite direction in the southern hemisphere.

The Caldecott medal, ______________ for the best children's picture book, is awarded each January.

The horn of the rhinoceros consists of a cone of tight bundles of keratin ______________ from the epidermis.

Most species of heliotropes are weeds, _______________ of them are cultivated.

Thunder occurs as ____________ through air, causing the heated air to expand and collide with layers of cooler air.

Researchers have long debated _____________ Saturn's moon Titan contains hydrocarbon oceans and lakes.

Nimbostratus clouds are thick, dark grey clouds __________ forebode rain.

_______________ in several early civilizations, a cubit was based on the length of the forearm from the tip of the middle finger to the elbow.

Only when air and water seep through its outer coat ___________.

___________ seasonal rainfall, especially in regions near the tropics, is winds that blow in an opposite direction in winter than in summer.

The extinct Martian volcano Olympus Mons is approximately three times as _____________ Mount Everest.

The flight instructor, ___________ at the air base, said that orders not to fight had been given.

In the northern and central parts of the state of Idaho ______________ and churning rivers.