Select the option that expresses the given sentence in passive voice.

The Smiths have put up a huge Christmas tree.

A huge Christmas tree has been put up by the Smiths.

The correct passive voice form of the given sentence "The Smiths have put up a huge Christmas tree" is A huge Christmas tree has been put up by the Smiths.

The active voice of the sentence is "The Smiths have put up a huge Christmas tree." This sentence is in the present perfect tense, which is used to describe an action that has happened in the past and is still relevant to the present. 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 "the Smiths" and the main verb is "put up." The past participle of "put up" is "put up." So, the passive form of the sentence is "A huge Christmas tree has been put up by the Smiths."

The other options are incorrect because:

• A huge Christmas tree is put up by the Smiths." This sentence is in the present tense, but the action of putting up a huge Christmas tree has already happened.
• A huge Christmas tree is being put up by the Smiths." This sentence is in the present progressive tense, which is used to describe an action that is happening now but is not finished. However, the action of putting up a huge Christmas tree is not happening now.
• A huge Christmas tree was put up by the Smiths." This sentence is in the simple past tense, but the action of putting up a huge Christmas tree is still relevant to the present.