如图为人的屈肘动作和伸肘动作示意图,与此有关的叙述正确的是( )
A:屈肘时,1肱二头肌舒张,2肱三头肌收缩
B:3是骨骼肌的肌腱,4是骨骼肌的肌腹
C:1和2相互配合,牵动骨完成屈肘或伸肘动作
D:听到口令做屈肘动作是通过神经中枢完成的
(I)求证:BE∥平面ACF;
(II)求平面BCF与平面BEF所成锐二面角的余弦角.
阅读短文,填入所缺单词完成句子
Today is afine day. The sun is shining in the sky. We are in the garden. We can see manybutterflies and birds in it. The butterflies are purple and the birds areyellow. They fly in the sky. The birds can sing well. We play on the slide andswing. We are very happy.
请你根据提示信息,写出相应的名称。