他想用努力证明自己不是小孩子了。

Tā xiǎng yòng nǔlì zhèngmíng zìjǐ bú shì xiǎoháizi le.

He wants to use hard work to prove that he is no longer a child.

这张照片可以证明我们去过北京。

Zhè zhāng zhàopiàn kěyǐ zhèngmíng wǒmen qùguò Běijīng.

This photo can prove that we have been to Beijing.

我会用行动证明我对你的爱。

Wǒ huì yòng xíngdòng zhèngmíng wǒ duì nǐde ài.

I will prove my love for you with my actions.