I believe the answer is "D" something else.
For all weapons, to shoot directly at the target formation you need to have LoS and range to unit(s) in that formation. But after this, the rules for "normal" weapons differ from "Barrage" weapons.

• For normal weapons, the player must declare for each weapon type whether it is shooting at units in cover or out of cover (so all AP, or AT, or MW shooting). The -1 applies if shooting at any enemy unit that is in cover or partially obscured to *all* firing units.
  Note, hits would be allocated to *all* enemy of the target type that are in range and LoS of at least one firer.
  
  
• If using barrage template, the 'target unit' must be covered, so must be 'seen' by all firers. However, when rolling for hits under the template, you dice for each unit separately considering the situation of each; three are in or behind cover and get the -1, potentially the 'target unit' may also get the -1 if it was partially obscured.
  (so almost "c", but not quite)