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31. According to band theory, a semiconductor is a material which has a(an)_________ valence band, a(an) conduction band, and between them. a. completely filled; completely filled; a wide gap b. empty; partially filled; a narrow gap c. partially filled; partially filled; a wide gap d. partially filled; empty; a narrow gap e. partially filled; empty; no gap
60. The structural strength of cement is the result of a. its high density. b. the endothermic reactions used in manufacturing it. c. the varying properties of different materials in each layer. d. formation of networks with large surface areas and strong attractions to each other. e. freedom of motion of valence electrons among nuclei which are held firmly in place. 61. Three classifications of ceramics include those made from clay, called alumina and magnesia, called ceramics. a. glass; nonoxide; silicate b. cement; oxide; glass c. nonoxide; silicate; oxide d. silicate; oxide; nonoxide e. composite; silicate; oxide ceramics; those made of ceramics; and those made of nitrides and carbides, called