下面四图中昼夜温差最大的是
A.A
B.B
C.C
D.D
答案:C
下列哪一组是鸟类特有的特征( )
①体表有羽毛②用肺呼吸并用气囊辅助呼吸③体温恒定④通过产卵繁殖后代⑤前肢覆羽成翼⑥善于飞行.
A.①③⑥
B.②③④
C.①②⑤
D.②⑤⑥
By studying hard and _____, you will achieve your dream. [ ]
A. give up
B. giving up
C. not giving up
D. not to give up