Subject + 向 + Person + 保证 + Clause
The verb 保证 (bǎozhèng) means "to guarantee," "to assure," or "to promise" in Chinese. It is used when someone gives their word or makes a firm commitment about something. It can be followed by a clause describing what is being guaranteed.
我保证下次不会迟到了。
Wǒ bǎozhèng xià cì bù huì chídào le.
I promise I won't be late next time.
他保证这个产品的质量没有问题。
Tā bǎozhèng zhège chǎnpǐn de zhìliàng méiyǒu wèntí.
He guarantees there are no quality issues with this product.
我可以保证这件事是真的。
Wǒ kěyǐ bǎozhèng zhè jiàn shì shì zhēn de.
I can guarantee that this matter is true.