他一定会来的。

Tā yídìng huì lái de.

He will certainly come.

你一定要吃药。

Nǐ yídìng yào chī yào.

You must have medicine.

明天你一定要来参加会议。

Míngtiān nǐ yídìng yào lái cānjiā huìyì.

You must come to the meeting tomorrow.