Which courts have original jurisdiction over nearly all civil and criminal cases heard in federal courts?

Option B is the answer - district courts

Explanation:

District courts, a type of courts found in several nations, serve as trail courts of the federal system in those countries. They have 'original jurisdiction' over most of the criminal cases involving murder and kidnapping of persons, and civil cases such as disagreements between groups and private individuals over properties or money.

Sometimes, these courts are referred to as 'small case courts' due to the type of cases been brought before them as the lowest level of the legal hierarchy.