The question gives no indication as to which type of migraine is more common, so B is not correct. C is not correct; we know that siblings of classical migraine sufferers are more likely to have classical migraines, regardless of their spouse. The question doesn't mention children at all, so D is out of scope. There is also nothing in the passage to indicate that E should be true.

The correct answer is A. Siblings and spouses of common migraine sufferers are both twice as likely to suffer common migraines. Since spouses are not related by heredity, this suggests that some environmental factor is involved. On the other hand, someone is four times more likely to suffer a classical migraine if they have a sibling who does, but no more likely if their spouse does. Siblings are related by heredity; spouses are not. This suggests heredity plays a role in classical migraines.