2016年5月10日SAT考试阅读题

今天为大家带来2016年5月10日SAT考试阅读题附答案和解析，希望可以帮助到考生们。

SAT考试阅读题目Critical Reading>Select an Answer

　　Plants, and all other living things, require nitrogen for growth; it is anessential component of nucleic acids and proteins. Although air is mostlynitrogen, this gaseous form is inaccessible to plants and must be fixed intoammonium to render it biologically relevant. Soil bacteria called rhizobia fixnitrogen, but to do this they must first take up residence inside the roots oflegumes like pea, alfalfa, clover, and soybean.

　　Soon after a legume begins to grow, rhizobia invade its root hairs andmultiply, causing the plant to form specialized organs—nodules—that contain theproliferating bacteria. This symbiotic arrangement benefits both parties:legumes can thrive without nitrogen fertilizers only if they have functionalnitrogen-fixing nodules, while the bacteria receive the energy needed tomultiply and fix nitrogen from the plant. When the plant dies, the fixednitrogen is released into the soil so other plants can use it. This process hassignificant implications for agriculture, as nitrogen is the most commonnutrient deficient in the earth's soil and, thus, the one most commonlysupplied by chemical fertilizers.

　　Rhizobia are a diverse group taxonomically, genetically, andmetabolically. They can be found in distant genera. Their symbiotic traitappears to have arisen independently multiple times by horizontal transfer ofgenes. However, it is not thought that this horizontal gene transfer issufficient to confer symbiosis, or to explain the biodiversity of rhizobia.There must be selective pressures preventing or permitting the expression ofthe acquired symbiosis trait and adaptive mechanisms to deal with these pressures.But neither the pressures nor the measures taken to circumvent them are known.

　　The underlined word "relevant" most nearly means __________

　　(A) connected.

　　(B) linked.

　　(C) useable.

　　(D) pertinent.

　　答案：C

　　解析：

　　Choice C is the best answer. The author states that the gaseous form ofnitrogen "is inaccessible to plants and must be fixed into ammonium torender it biologically relevant." In this context, "relevant"most nearly means "useable." The author’s point is that the nitrogenmust be in a form that is biologically useable or accessible to plants.

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