每个健康公民都应该积极参加义务献血,通常一次献血量为( )
A:20﹣30mL
B:1000mL
C:2000mL
D:200﹣400mL
读图“地震波速度与地球内部构造图”,完成下题.
He lives _______, but he never feels _______, because he likes reading.