A:①③
B:①②
C:①④
D:②④
下面甲、乙两图分别表示大草履虫和双小核草履虫单独培养(甲)和混合培养(乙)时的种群增长速度。从两图所示的结果可以推断( )
The movie covers all of Chinese history. It is _______ worth seeing again.