基因型为AaBBccDD的二倍体生物，可产生不同基因型的配子种类数是（）
A.2
B.4
C.8
D.16
参考答案：A
已知噪声源1的声压级为80 dB，噪声源2的声压级也为60 dB，则两个噪声源叠加后的声压级为( )dB。
A．140
B．80
C．81
D．70
(2010·上海)Wind power is an ancient source of energy ________ we may return in the near future.
A．on which
B．by which
C．to which
D．from which
