When may a scientific theory be revised? O never, once it has been published
O when a single experiment's data goes against it
when a new hypothesis provides a better explanation
O after a large amount of data refutes it

The roman empire fell around the 5th century, and as islam spread in the 7th century, trade between europe and china slowed. chinese traders were blocked from westward expansion into europe when the chinese army was defeated by muslim fighters in the area known as syr darya. the trade routes, known as the silk road, fell into disuse, and trade between the far east and europe nearly stopped. it wasn't until the 13th century when the mongols invaded and controlled central asia and large parts of the middle east that extensive trade along these routes was opened again. based upon the paragraph above and your knowledge of the mongols, which of the following statements is correct? a. the mongols unified regions along the silk road, allowing for safe transport of goods. b. muslims controlled busy trade routes into china from the 5th to the 7th centuries. c. without access to european markets, the chinese were unable to obtain raw materials. d. the mongols replaced the roman empire as the dominant force in western europe.

Which statement describes absolute and apparent brightness? absolute brightness and apparent brightness are identical ways to describe the brightness of a star. absolute brightness and apparent brightness change with the distance from the star to the observer. absolute brightness depends on the distance from the star to the observer, whereas apparent brightness is always the same. absolute brightness is the actual amount of light produced by the star, whereas apparent brightness changes with distance from the observer.

17. a graduated standard used to evaluate student achievement is called a: a. rubric b. norm-referenced test c. criterion-referenced test d. multiple-choice question e. guessing penalty