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

• There may be an oncoming vehicle that is passing the snowplow using your lane.
  Explanation:

  "When a snowplow is approaching from the opposite direction, look ahead in your lane carefully. There may be an oncoming vehicle that is passing the snowplow using your lane."
• There may be an oncoming vehicle that is passing the snowplow using the same lane as the snowplow.
• There may be an oncoming vehicle going faster than the snowplow.
• All of the above.