50. (1) Then, I drive to the old neighborhood where I lived when I was a child. (2) I cruise the main street in the small town and then drive to visit my junior high school. (3) Longing for things to stay as they are, I look at every view of the farms as a work of art. (4) My chemistry teacher is still gentle, outspoken, and optimistic. (5) I drop in on my first chemistry teacher, with whom I have always kept in touch. (A) 31254 (B) 24315 (C) 21345 (D) 34125

47. We take our smoothly paved highways and streets for granted as products of technology and engineering. They are made of concrete, a building material composed of cement, sand or gravel, and water. (A) The huge concrete channel supplied drinking water to ancient Rome. (B) The cement in concrete has a long history. The Egyptians burned chips from the Great Pyramid and used the resulting ash as mortar. (C) The Romans made a cement out of volcanic ash, which they turned into concrete by mixing it with water, lime, and rock; they used cement in the Great Aqueduct about 2000 years ago. (D) Today, concrete mix containing sand is used for smooth applications; gravel mix is used where a stronger concrete is required.

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