He often goes to school (B.on) his bike. 他经常骑自行车上学. 骑自行车,可以表达成by bike（中间不加任何冠词或是物主代词）,或on one's bike（one's,某人的,可以用物主代词,或是定冠词the）.因为这里有定冠词the,所以不能用by,而是on.
