下图是某地区广东松的种群年龄结构调查结果,该种群的最终发展趋势是
A.总能量增加
B.种群密度下降
C.环境阻力不变
D.该种群总能量降低
BD
The number of giant pandas is getting _________ because their living areas are becoming farmlands.
A.less and less
B.larger and larger
C.smaller and smaller
D.fewer and fewer
自动空气制动机的基本原理是:向制动管()时,制动机产生缓解作用;当制动管减压时,制动机产生制动作用。