提一桶水上楼,这时手臂上肱二头肌和肱三头肌的状态分别是()
A:收缩,收缩
B:收缩,舒张
C:舒张,收缩
D:舒张,舒张
An advertisement uses words and pictures to ____ people to buy a product or service, or to believe in an idea.
如图,在平面直角坐标系中,四边形OABC是平行四边形,O(0,0),A(1,﹣2),B(3,1),则C点坐标为____
“螳螂捕蝉,黄雀在后”这一食物链可以准确的表述为( )