由图可知,蛙卵孵化的最适温度是( )
A:15℃
B:20℃
C:25℃
D:30℃
《中国新工业发展史大纲》中说:“国人居此恶劣环境之下……停厂者有之,杀生破家者有之,遂酿成民国十年之经济恐慌。”导致这一“经济恐慌”的主要原因是
The desk that ____ clean so I could do homework was always surrounded with bowls of bad milk, old magazines and so on.
人类祖先与猿分界的重要标志是( )