-- Do you know ______ our Chinese National Symbol of Day （国家公祭日） is?
-- Yes, it's on December 13th. It's in memory of the people_____ were killed in Nanjing Massacre.
A：whether; that
B：when; who
C：how; which
D：why; that
辨别下面所叙述的几种事实
①一个乳酸菌
②培养皿中的乳酸菌菌落
③培养基被污染后，除乳酸菌外，又滋生了真菌以及大肠杆菌等其他细菌．
回答下列问题：它们各属于生命系统的哪项结构层次？
①____ ；②____；③____．
