2. The unused genes in differentiated cells are neither destroyed nor mutated (they retain the potential for being expressed)
3. Only a small percentage of the genome is expressed in each cell, and a portion of the RNA synthesized in each cell is specific for that cell type.
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Read the passage below. Then, answer the questions.
Fossil Fuels All fossil fuels form from the buried remains of ancient organisms. But different types of fossil fuels form in different ways and from different types of organisms. Petroleum and natural gas form mainly from the remains of microscopic sea life. When these organisms die, their remains collect on the ocean floor, where they are buried by sediment. Over time, the sediment slowly becomes rock and traps the organic remains. Through physical and chemical changes over millions of years, the remains become petroleum and natural gas. Gradually, more rocks form above the rocks that contain the fossil fuels. Under the pressure of overlying rocks and sediments, the fossil fuels are able to move through permeable rocks. Permeable rocks are rocks that allow fluids, such as petroleum and natural gas, to move through them. These permeable rocks become reservoirs that hold petroleum and natural gas.
Which of the following statements can be inferred from the information in the passage?
A. Fossil fuel formation is ongoing, and current remains may become petroleum in the future.
B. Fossil fuel formation happened millions of years ago and no longer takes place today.
C. Current petroleum and natural gas reservoirs are found only beneath the ocean floor.
D. Permeable rocks are also a good place to find other fossil fuels, such as coal.