shàng / lóu / tī / shí / tā / xiān / mài / chū / qián / jiǎo / zài / bǎ / shēn / tǐ / de / zhòng / xīn / yí / shàng / qù

上楼梯时，他先迈出前脚，再把身体的重心移上去。

When climbing the stairs, he puts his leading foot forward first and then shifts his weight onto it.