ACT真題每日一練12.7

　　Science Question for Monday, December 7th, 2015

　　Passage I

　　The following table represents the concentration of ions and dissolved gases in the sediment at the bottom of an ocean. A depth of 0 centimeters (cm) represents the top of the sediment. The concentrations are expressed in parts per million (ppm). The acidity of a solution is represented on a scale known as pH. A pH of 1 is very acidic, a pH of 7 is neutral, and a pH of 14 is very basic.

　　Table adapted from R.M. Atlas and R. Bartha, Microbial Ecology: Fundamentals and Applications.

　　©1981 by Addison-Wesley Publishing Company.

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　　According to the information provided in the table, the concentration of which of the following ions and dissolved gases is constant for sediment depths of 10 cm or more?

　　A. Sulfide (S2–)

　　B. Carbon dioxide (CO2)

　　C. Ferric iron (Fe3+)

　　D. Oxygen (O2)