根据数值进行换算:
My father often does many kinds of sports, such as ____ (playing/to play) football and swimming.
如图3所示,用一张硬卡片先后快拨和慢拨木梳的齿,听到卡片声音发生变化.这个实验用来探究 ( )
每个健康的公民,都应该积极参加献血,通常一次献血的量为