For writing a polite form we can :use
•You must do it
•_would you like to
• ! come here

The option that shows politeness is:

Would you like to

Explanation:

The first option, because of the use of "must", conveys sternness, while the third option, which is an imperative sentence, conveys a command, an order.

However, the second option shows politeness and care in addressing the interlocutor. "Would like" is a softer way to express that you or someone else want something. Take a look at the examples below to see how much more polite and careful the sentences sound when employing "would like":

- Do you want to have some tea? → Would you like to have some tea?

- I want to talk to you. → I would like to talk to you.