How to define a dropdown on a form?

Atlas Form
1 
{
  "id": "internalRating",
  "type": "select",
  "label": "Internal Rating",
  "sectionId": "admin",
  "order": 30,
  "width": "quarter",
  "config": {
    "options": [
      { "value": "A", "label": "A — Premium" },
      { "value": "B", "label": "B — Standard" },
      { "value": "C", "label": "C — At Risk" },
      { "value": "D", "label": "D — Churned" }
    ]
  }
}