gāng / kāishǐ / měitiān / pǎobù / hěn / xīnkǔ / dàn / jiǔ'érjiǔzhī / wǒ / de / tǐlì / míngxiǎn / tígāo / le

刚开始每天跑步很辛苦，但久而久之，我的体力明显提高了。

Running every day was difficult at first, but over time my stamina improved noticeably.