The correct passive form of the given sentence is Mira might have been delayed by the snow-storm.

The active voice of the sentence is "The snow-storm might have delayed Mira." This sentence is in the past modal perfect tense, which is used to describe an action that might have 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 "Mira" and the main verb is "delay." The past participle of "delay" is "delayed." So, the passive form of the sentence is "Mira might have been delayed by the snow-storm."

The other options are incorrect because:

• Mira may be delayed by the snow-storm." This sentence is in the present modal tense, which is used to describe an action that may happen in the future. However, the sentence is talking about an action that might have happened in the past.
• Mira might be delayed by the snow-storm." This sentence is in the past modal tense, but the verb is in the present tense. The verb should be in the past tense to match the tense of the rest of the sentence.
• Mira may have been delayed by the snow-storm." This sentence is also in the past modal perfect tense, but the verb "may" is used to describe an action that is likely to happen. However, the sentence is talking about an action that might have happened, but is not likely to have happened.