The correct active form of the given sentence is Special commandos surrounded the building.

The sentence "The building was surrounded by special commandos" is in the passive voice. The passive voice 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 building" and the main verb is "surround." The past participle of "surround" is "surrounded." So, the passive form of the sentence is "The building was surrounded by special commandos."

The active voice is formed by putting the subject of the passive sentence before the verb and the past participle of the main verb. In this case, the subject of the passive sentence is "special commandos" and the main verb is "surround." The past participle of "surround" is "surrounded." So, the active form of the sentence is Special commandos surrounded the building.

The other options are incorrect because:

• Special commandos have surrounded the building is in the present perfect tense, while the original sentence is in the past tense.
• Special commandos are surrounding the building is in the present progressive tense, while the original sentence is in the simple past tense.
• Special commandos surround the building is grammatically incorrect. The verb "to surround" requires a direct object, but the phrase "special commandos surround" does not have a direct object.