Select the correct passive form of the given sentence.

He built a website from scratch.

A website was built from scratch by him.

The correct passive form of the given sentence is A website was built from scratch by him.

The active voice of the sentence is He built a website from scratch. This sentence is in the simple past tense, which is used to describe an action that happened in the past. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "he" and the main verb is "build." The past participle of "build" is "built." So, the passive form of the sentence is A website was built from scratch by him.

The other options are incorrect because:

• A website has been built from scratch by him. is in the present perfect tense, which is used to describe an action that has happened in the past but is still relevant to the present. The website has already been built, so the present perfect tense is not appropriate.
• A website was building from scratch by him. is in the present progressive tense, which is used to describe an action that is happening now but is not finished. The sentence is describing an action that happened in the past, so the present progressive tense is not appropriate.
• A website is built from scratch by him. is in the present tense, but the present tense is not appropriate for an action that happened in the past.