1、在等差数列中，则=(　　 )

A．10　　　　　 B．19　　　　　　 C．11　　　　　　 D．17

84. A new kind of mouse was produced ,which is twice large than normal .

83. By controlling the production of human growth hormone .

82. To expect food animals that grow faster and larger or produce more milk or eggs.

81. 4　　

77. Economic impact　　 78. Boosting/ High death rate　

74. Nil rainfall　　 75. Deforestation　 　　76. Overgrazing of livestock　

71. Desertification　 72. affectcing human life　 73. Climate changes