A:自然选择的结果
B:无翅或残翅昆虫繁殖能力强
C:人工选择的结果
D:有翅昆虫被天敌捕食
“通过封建契约和分封仪式,如臣服礼、授职礼,领主和附庸形成依附关系。”材料体现的制度是( )
读图回答下题。
Don't give up doing something if you have decided to do it.