Why should you look ahead carefully when a snowplow is approaching from the opposite direction?

• An oncoming vehicle might be passing the snowplow using your lane.
  Explanation:

  "When a snowplow is approaching from the opposite direction, always look ahead carefully in your lane. Another vehicle might be attempting to pass the snowplow and could enter your lane, creating a dangerous situation."
• An oncoming vehicle might be passing the snowplow in the snowplow’s lane
• An oncoming vehicle might be speeding faster than the snowplow
• All of the above.