明适应过程即视网膜上感光细胞的光感受性_________的过程。
参考答案:降低
With the advances of technology, plastics have taken the place of many ______ materials. [ ]
A. conventional
B. optional
C. artificial
D. potential
我国铁路客车车次为双号,表明该列车( )
A.由南向北行驶
B.由北向南行驶
C.向远离北京的方向行驶
D.向接近北京的方向行驶