What are the relative compositions of the materials from which stars form?
A. about 2% hydrogen, about 74% helium, no more than 24% other materials
B. about 74% hydrogen, about 24% helium, no more than 2% other materials
C. about 24% hydrogen, about 74% helium, no more than 2% other materials
D. Stars have vastly differing combinations of materials.
Answer: B
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Turbulent wind flow that blows over a barren surface can pick up sediment by the process known as ____________________
Fill in the blank(s) with correct word
Managing crop competitors and pests has been challenging to agronomists for centuries. One approach, integrated pest management, ________
A) uses no pesticides of any kind B) uses only natural pesticides C) combines synthetic chemical pesticides with biocontrol techniques D) uses only synthetic chemical pesticides E) combines a variety of pesticides to combat the pest
What property of carbon allows for the formation of so many different organic molecules?
A. Carbon resides in the exact middle of the periodic table, from left to right, with exactly the same number of reactive elements on either side of it. It can therefore react with the maximum number of elements. B. Carbon atoms are unique in their ability to form strong chemical bonds repeatedly with other carbon atoms, which permits the formation of countless possible structures. C. Carbon forms three different isotopes which allows for the formation of many more molecules than other elements. D. Carbon atoms uniquely contain exactly the same number (six) of protons, neutrons, and electrons in their atomic structure.
Sea floor is formed at spreading ridges and destroyed
A. by magnetic-field reversals. B. in subduction zones. C. in transform faults. D. at divergent boundaries.