user
Instruction
Answer the question based on the provided table.


Table
Table Title: George Bush Intercontinental Airport
Table Content:
| Rank | City | Passengers | Top Carriers |
| --- | --- | --- | --- |
| 1 | Los Angeles, CA | 700,000 | American, Spirit, United |
| 2 | Chicago, IL | 673,000 | American, Spirit, United |
| 3 | Denver, CO | 654,000 | Frontier, Spirit, United |
| 4 | San Francisco, CA | 492,000 | United |
| 5 | Dallas/Fort Worth, TX | 488,000 | American, United |
| 6 | Newark, NJ | 480,000 | United |
| 7 | Las Vegas, NV | 442,000 | Spirit, United |
| 8 | Charlotte, NC | 441,000 | United, US Airways |
| 9 | Atlanta, GA | 400,000 | Delta, United |
| 10 | Phoenix, AZ | 393,000 | United, US Airways |


Question
which is the busiest domestic route out of houston intercontinental airport that does not have an american flight?


Answer Format
The final answer should be concise and use the following format:
```json
{
    "answer": [
        "answer1",
        "answer2",
        ...
    ]
}
```
rule
["Denver, CO"]