The background extinction rate is
1.the rate at which new species appear.
2.the rate at which species are always becoming extinct.
3.a time when many species become extinct.
4.a time when no species becomes extinct.
5.a time when species living in the dark become extinct.
2
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In the neritic zone, a 10-milliliter sample of surface water can contain ____ of multicellular planktonic organisms
a. hundreds b. thousands c. millions d. billions e. trillions
The chemotherapy drug taxol inhibits the breakdown of microtubules. A cell treated with taxol would become stuck right after which phase?
A. metaphase B. anaphase C. cytokinesis D. telophase E. prophase
Mature soil generally has three horizons. Label the soil horizons A, B, and C in the following picture. In addition, describe the contents of the horizons by labeling D through G. 
D. ________E. ________F. ________G. ________
What will be an ideal response?
Smooth muscle
A) contracts when stretched. B) is under voluntary control. C) does not contain actin or myosin. D) produces rapid contractions.