如果要用实验证明叶绿体是光合作用的场所,最好用下列哪项做实验( )
A.不含叶绿素的叶片
B.用酒精加热过的叶片
C.有白斑或白条纹的叶片
D.全绿色的叶片
答案:C
---Tom almost ran into a pole yesterday while driving on the highway.
--- I suppose he ____ too fast.
A.had driven
B.was driving
C.must drive
D.should have driven
国际上通常认为()岁及以上人口数占总人口数()以上者的国家为老年型人口国家。