我看得出来他们的关系听密切的。

Wǒ kàn de chūlái tāmen de guānxì tīng mìqiè de.

I can tell their relationship is pretty close.

我们之间的合作非常密切，共同努力可以取得更好的成果。

Wǒmen zhī jiān de hézuò fēicháng mìqiè, gòngtóng nǔlì kěyǐ qǔdé gèng hǎo de chéngguǒ.

The cooperation between us is very close, and joint efforts can yield better results.

请保持与老师的密切联系，及时解决学习中的问题。

Qǐng bǎochí yǔ lǎoshī de mìqiè liánxì, jíshí jiějué xuéxí zhōng de wèntí.

Please maintain close contact with the teacher and promptly address any learning issues.