Question

Active to passive 1- You must do it at once. 2- One should keep one's promise.

Answer 1

it must be done at once by you
promises should be kept

Answer 2

Before beginning let us first know what are active and passive voices:

Active voice - A type sentence where in the subject of the sentence precede the object of the sentence.

Passive voice - A type of sentence wherein the object of the sentence precede the subject of the sentence.

Given sentence:

1. You must do it at once.

2. One should keep one's promises.

Passive voice of the given sentence:

1. It must be done at once by you. (Note: "by you" can be ignored)

2. Promises should be kept. OR One's promises should be kept OR One's promises should kept by one.