A：keeping control of thoughts is very difficult
B：thinking is a kind of activity limited to humans
C：mammals evolved much more slowly than humans
D：mammals had poor awareness of dangers and opportunities
全国性的抗日战争爆发的标志是（ ）
猫喜欢玩球。
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用机械方法分离某细胞器的各种成分，对分离的成分用双缩脲试剂和甲基绿—毗罗红试剂检测。发现能够使双缩脲试剂呈现紫色反应，使甲基绿—吡罗红试剂呈现红色反应。则该细胞器最可是（）
