How do you say

He had been training hard for the upcoming marathon for the past three months.

..in Chinese?

他在过去三个月一直在认真训练，为即将到来的马拉松比赛做准备。

tā zài guò qù sān gè yuè yì zhí zài rèn zhēn xùn liàn ， wèi jí jiāng dào lái de mǎ lā sōng bǐ sài zuò zhǔn bèi 。

How do you say "I am going to buy a new sweater." in Chinese?